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)

 Re·li·gion n.
 1. The outward act or form by which men indicate their recognition of the existence of a god or of gods having power over their destiny, to whom obedience, service, and honor are due; the feeling or expression of human love, fear, or awe of some superhuman and overruling power, whether by profession of belief, by observance of rites and ceremonies, or by the conduct of life; a system of faith and worship; a manifestation of piety; as, ethical religions; monotheistic religions; natural religion; revealed religion; the religion of the Jews; the religion of idol worshipers.
    An orderly life so far as others are able to observe us is now and then produced by prudential motives or by dint of habit; but without seriousness there can be no religious principle at the bottom, no course of conduct from religious motives; in a word, there can be no religion.   --Paley.
    Religion [was] not, as too often now, used as equivalent for godliness; but . . . it expressed the outer form and embodiment which the inward spirit of a true or a false devotion assumed.   --Trench.
    Religions, by which are meant the modes of divine worship proper to different tribes, nations, or communities, and based on the belief held in common by the members of them severally.  . . .  There is no living religion without something like a doctrine.  On the other hand, a doctrine, however elaborate, does not constitute a religion.   --C. P. Tiele (Encyc. Brit.).
    Religion . . . means the conscious relation between man and God, and the expression of that relation in human conduct.   --J. Köstlin (Schaff-Herzog Encyc.)
    After the most straitest sect of our religion I lived a Pharisee.   --Acts xxvi. 5.
 The image of a brute, adorned
 With gay religions full of pomp and gold.   --Milton.
 2. Specifically, conformity in faith and life to the precepts inculcated in the Bible, respecting the conduct of life and duty toward God and man; the Christian faith and practice.
 Note: This definition is from the 1913 Webster, which was edited by Noah Porter, a theologian.  His bias toward the Christion religion is evident not only in this definition, but in others as well as in the choice of quations or illustrative phrases. Caveat lector. - PJC
    Let us with caution indulge the supposition that morality can be maintained without religion.   --Washington.
    Religion will attend you . . . as a pleasant and useful companion in every proper place, and every temperate occupation of life.   --Buckminster.
 3. R. C. Ch. A monastic or religious order subject to a regulated mode of life; the religious state; as, to enter religion.
    A good man was there of religion.   --Chaucer.
 4. Strictness of fidelity in conforming to any practice, as if it were an enjoined rule of conduct. [R.]
    Those parts of pleading which in ancient times might perhaps be material, but at this time are become only mere styles and forms, are still continued with much religion.   --Sir M. Hale.
 Note: ☞ Religion, as distinguished from theology, is subjective, designating the feelings and acts of men which relate to God; while theology is objective, and denotes those ideas which man entertains respecting the God whom he worships, especially his systematized views of God. As distinguished from morality, religion denotes the influences and motives to human duty which are found in the character and will of God, while morality describes the duties to man, to which true religion always influences. As distinguished from piety, religion is a high sense of moral obligation and spirit of reverence or worship which affect the heart of man with respect to the Deity, while piety, which first expressed the feelings of a child toward a parent, is used for that filial sentiment of veneration and love which we owe to the Father of all. As distinguished from sanctity, religion is the means by which sanctity is achieved, sanctity denoting primarily that purity of heart and life which results from habitual communion with God, and a sense of his continual presence.
 Natural religion, a religion based upon the evidences of a God and his qualities, which is supplied by natural phenomena. See Natural theology, under Natural.
 Religion of humanity, a name sometimes given to a religion founded upon positivism as a philosophical basis.
 Revealed religion, that which is based upon direct communication of God's will to mankind; especially, the Christian religion, based on the revelations recorded in the Old and New Testaments.

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From: Webster's Revised Unabridged Dictionary (1913)

 The·ol·o·gy n.; pl. Theologies   The science of God or of religion; the science which treats of the existence, character, and attributes of God, his laws and government, the doctrines we are to believe, and the duties we are to practice; divinity; (as more commonly understood) “the knowledge derivable from the Scriptures, the systematic exhibition of revealed truth, the science of Christian faith and life.”
    Many speak of theology as a science of religion [instead of =\“science of God”] because they disbelieve that there is any knowledge of God to be attained.\=   --Prof. R. Flint (Enc. Brit.).
    Theology is ordered knowledge; representing in the region of the intellect what religion represents in the heart and life of man.   --Gladstone.
 Ascetic theology, Natural theology. See Ascetic, Natural.
 Moral theology, that phase of theology which is concerned with moral character and conduct.
 Revealed theology, theology which is to be learned only from revelation.
 Scholastic theology, theology as taught by the scholastics, or as prosecuted after their principles and methods.
 Speculative theology, theology as founded upon, or influenced by, speculation or metaphysical philosophy.
 Systematic theology, that branch of theology of which the aim is to reduce all revealed truth to a series of statements that together shall constitute an organized whole. --E. G. Robinson (Johnson's Cyc.).

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From: WordNet (r) 2.0

 natural theology
      n : a theology that holds that knowledge of God can be acquired
          by human reason without the aid of divine revelation