Nat·u·ral a.
 1. Fixed or determined by nature; pertaining to the constitution of a thing; belonging to native character; according to nature; essential; characteristic; innate; not artificial, foreign, assumed, put on, or acquired; as, the natural growth of animals or plants; the natural motion of a gravitating body; natural strength or disposition; the natural heat of the body; natural color.
    With strong natural sense, and rare force of will.   --Macaulay.
 2. Conformed to the order, laws, or actual facts, of nature; consonant to the methods of nature; according to the stated course of things, or in accordance with the laws which govern events, feelings, etc.; not exceptional or violent; legitimate; normal; regular; as, the natural consequence of crime; a natural death; anger is a natural response to insult.
    What can be more natural than the circumstances in the behavior of those women who had lost their husbands on this fatal day?   --Addison.
 3. Having to do with existing system to things; dealing with, or derived from, the creation, or the world of matter and mind, as known by man; within the scope of human reason or experience; not supernatural; as, a natural law; natural science; history, theology.
    I call that natural religion which men might know . . . by the mere principles of reason, improved by consideration and experience, without the help of revelation.   --Bp. Wilkins.
 4. Conformed to truth or reality; as: (a) Springing from true sentiment; not artificial or exaggerated; -- said of action, delivery, etc.; as, a natural gesture, tone, etc. (b) Resembling the object imitated; true to nature; according to the life; -- said of anything copied or imitated; as, a portrait is natural.
 5. Having the character or sentiments properly belonging to one's position; not unnatural in feelings.
 To leave his wife, to leave his babes, . . .
 He wants the natural touch.   --Shak.
 6. Connected by the ties of consanguinity. especially, Related by birth rather than by adoption; as, one's natural mother.  “Natural friends.”
 7. Hence: Begotten without the sanction of law; born out of wedlock; illegitimate; bastard; as, a natural child.
 8. Of or pertaining to the lower or animal nature, as contrasted with the higher or moral powers, or that which is spiritual; being in a state of nature; unregenerate.
    The natural man receiveth not the things of the Spirit of God.   --1 Cor. ii. 14.
 9. Math. Belonging to, to be taken in, or referred to, some system, in which the base is 1; -- said of certain functions or numbers; as, natural numbers, those commencing at 1; natural sines, cosines, etc., those taken in arcs whose radii are 1.
 10. Mus. (a) Produced by natural organs, as those of the human throat, in distinction from instrumental music. (b) Of or pertaining to a key which has neither a flat nor a sharp for its signature, as the key of C major. (c) Applied to an air or modulation of harmony which moves by easy and smooth transitions, digressing but little from the original key.  (d) Neither flat nor sharp; -- of a tone. (e) Changed to the pitch which is neither flat nor sharp, by appending the sign as, A natural.
 Natural day, the space of twenty-four hours.
 -- Natural fats, Natural gas, etc. See under Fat, Gas. etc.
 Natural Harmony Mus., the harmony of the triad or common chord.
 Natural history, in its broadest sense, a history or description of nature as a whole, including the sciences of botany, Zoology, geology, mineralogy, paleontology, chemistry, and physics. In recent usage the term is often restricted to the sciences of botany and Zoology collectively, and sometimes to the science of zoology alone.
 Natural law, that instinctive sense of justice and of right and wrong, which is native in mankind, as distinguished from specifically revealed divine law, and formulated human law.
 Natural modulation Mus., transition from one key to its relative keys.
 Natural order. Nat. Hist. See under order.
 Natural person. Law See under person, n.
 Natural philosophy, originally, the study of nature in general; the natural sciences; in modern usage, that branch of physical science, commonly called physics, which treats of the phenomena and laws of matter and considers those effects only which are unaccompanied by any change of a chemical nature; -- contrasted with mental philosophy and moral philosophy.
 Natural scale Mus., a scale which is written without flats or sharps.
 Note: Model would be a preferable term, as less likely to mislead, the so-called artificial scales (scales represented by the use of flats and sharps) being equally natural with the so-called natural scale.
 Natural science, the study of objects and phenomena existing in nature, especially biology, chemistry, physics and their interdisciplinary related sciences; natural history, in its broadest sense; -- used especially in contradistinction to social science, mathematics, philosophy, mental science or moral science.
 Natural selection Biol., the operation of natural laws analogous, in their operation and results, to designed selection in breeding plants and animals, and resulting in the survival of the fittest; the elimination over time of species unable to compete in specific environments with other species more adapted to survival; -- the essential mechanism of evolution.  The principle of natural selection is neutral with respect to the mechanism by which inheritable changes occur in organisms (most commonly thought to be due to mutation of genes and reorganization of genomes), but proposes that those forms which have become so modified as to be better adapted to the existing environment have tended to survive and leave similarly adapted descendants, while those less perfectly adapted have tended to die out through lack of fitness for the environment, thus resulting in the survival of the fittest. See Darwinism.
 Natural system Bot. & Zool., a classification based upon real affinities, as shown in the structure of all parts of the organisms, and by their embryology.
    It should be borne in mind that the natural system of botany is natural only in the constitution of its genera, tribes, orders, etc., and in its grand divisions.   --Gray.

 Natural theology, or Natural religion, that part of theological science which treats of those evidences of the existence and attributes of the Supreme Being which are exhibited in nature; -- distinguished from revealed religion. See Quotation under Natural, a., 3.
 Natural vowel, the vowel sound heard in urn, furl, sir, her, etc.; -- so called as being uttered in the easiest open position of the mouth organs. See Neutral vowel, under Neutral and Guide to Pronunciation, § 17.
 Syn: -- See Native.

From: Webster's Revised Unabridged Dictionary (1913)

 Or·der n.
 1. Regular arrangement; any methodical or established succession or harmonious relation; method; system; as: (a) Of material things, like the books in a library. (b) Of intellectual notions or ideas, like the topics of a discource. (c) Of periods of time or occurrences, and the like.
    The side chambers were . . . thirty in order.   --Ezek. xli. 6.
    Bright-harnessed angels sit in order serviceable.   --Milton.
    Good order is the foundation of all good things.   --Burke.
 2. Right arrangement; a normal, correct, or fit condition; as, the house is in order; the machinery is out of order.
 3. The customary mode of procedure; established system, as in the conduct of debates or the transaction of business; usage; custom; fashion.
 And, pregnant with his grander thought,
 Brought the old order into doubt.   --Emerson.
 4. Conformity with law or decorum; freedom from disturbance; general tranquillity; public quiet; as, to preserve order in a community or an assembly.
 5. That which prescribes a method of procedure; a rule or regulation made by competent authority; as, the rules and orders of the senate.
    The church hath authority to establish that for an order at one time which at another time it may abolish.   --Hooker.
 6. A command; a mandate; a precept; a direction.
    Upon this new fright, an order was made by both houses for disarming all the papists in England.   --Clarendon.
 7. Hence: A commission to purchase, sell, or supply goods; a direction, in writing, to pay money, to furnish supplies, to admit to a building, a place of entertainment, or the like; as, orders for blankets are large.
    In those days were pit orders -- beshrew the uncomfortable manager who abolished them.   --Lamb.
 8. A number of things or persons arranged in a fixed or suitable place, or relative position; a rank; a row; a grade; especially, a rank or class in society; a group or division of men in the same social or other position; also, a distinct character, kind, or sort; as, the higher or lower orders of society; talent of a high order.
    They are in equal order to their several ends.   --Jer. Taylor.
    Various orders various ensigns bear.   --Granville.
    Which, to his order of mind, must have seemed little short of crime.   --Hawthorne.
 9. A body of persons having some common honorary distinction or rule of obligation; esp., a body of religious persons or aggregate of convents living under a common rule; as, the Order of the Bath; the Franciscan order.
 Find a barefoot brother out,
 One of our order, to associate me.   --Shak.
    The venerable order of the Knights Templars.   --Sir W. Scott.
 10. An ecclesiastical grade or rank, as of deacon, priest, or bishop; the office of the Christian ministry; -- often used in the plural; as, to take orders, or to take holy orders, that is, to enter some grade of the ministry.
 11. Arch. The disposition of a column and its component parts, and of the entablature resting upon it, in classical architecture; hence (as the column and entablature are the characteristic features of classical architecture) a style or manner of architectural designing.
 Note: ☞ The Greeks used three different orders, easy to distinguish, Doric, Ionic, and Corinthian.  The Romans added the Tuscan, and changed the Doric so that it is hardly recognizable, and also used a modified Corinthian called Composite.  The Renaissance writers on architecture recognized five orders as orthodox or classical, -- Doric (the Roman sort), Ionic, Tuscan, Corinthian, and Composite. See Illust. of Capital.
 12. Nat. Hist. An assemblage of genera having certain important characters in common; as, the Carnivora and Insectivora are orders of Mammalia.
 Note: ☞ The Linnaean artificial orders of plants rested mainly on identity in the numer of pistils, or agreement in some one character.  Natural orders are groups of genera agreeing in the fundamental plan of their flowers and fruit.  A natural order is usually (in botany) equivalent to a family, and may include several tribes.
 13. Rhet. The placing of words and members in a sentence in such a manner as to contribute to force and beauty or clearness of expression.
 14. Math. Rank; degree; thus, the order of a curve or surface is the same as the degree of its equation.
 Artificial order or Artificial system. See Artificial classification, under Artificial, and Note to def. 12 above.
 Close order Mil., the arrangement of the ranks with a distance of about half a pace between them; with a distance of about three yards the ranks are in open order.
 The four Orders, The Orders four, the four orders of mendicant friars. See Friar. --Chaucer.
 General orders Mil., orders issued which concern the whole command, or the troops generally, in distinction from special orders.
 Holy orders. (a) Eccl. The different grades of the Christian ministry; ordination to the ministry. See def. 10 above. (b) R. C. Ch. A sacrament for the purpose of conferring a special grace on those ordained.
 In order to, for the purpose of; to the end; as means to.
    The best knowledge is that which is of greatest use in order to our eternal happiness.   --Tillotson.

 Minor orders R. C. Ch., orders beneath the diaconate in sacramental dignity, as acolyte, exorcist, reader, doorkeeper.
 Money order. See under Money.
 Natural order. Bot. See def. 12, Note.
 Order book. (a) A merchant's book in which orders are entered. (b) Mil. A book kept at headquarters, in which all orders are recorded for the information of officers and men. (c) A book in the House of Commons in which proposed orders must be entered. [Eng.]
 Order in Council, a royal order issued with and by the advice of the Privy Council. [Great Britain]
 Order of battle Mil., the particular disposition given to the troops of an army on the field of battle.
 Order of the day, in legislative bodies, the special business appointed for a specified day.
 Order of a differential equation Math., the greatest index of differentiation in the equation.
 Sailing orders Naut., the final instructions given to the commander of a ship of war before a cruise.
 Sealed orders, orders sealed, and not to be opened until a certain time, or arrival at a certain place, as after a ship is at sea.
 Standing order. (a) A continuing regulation for the conduct of parliamentary business. (b) Mil. An order not subject to change by an officer temporarily in command.
 To give order, to give command or directions. --Shak.
 To take order for, to take charge of; to make arrangements concerning.
    Whiles I take order for mine own affairs.   --Shak.
 Syn: -- Arrangement; management. See Direction.

From: WordNet (r) 2.0

 natural order
      n : the physical universe considered as an orderly system
          subject to natural (not human or supernatural) laws