natural gas
 天然氣


 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)

 Gas n.; pl. Gases
 1. An aëriform fluid; -- a term used at first by chemists as synonymous with air, but since restricted to fluids supposed to be permanently elastic, as oxygen, hydrogen, etc., in distinction from vapors, as steam, which become liquid on a reduction of temperature. In present usage, since all of the supposed permanent gases have been liquified by cold and pressure, the term has resumed nearly its original signification, and is applied to any substance in the elastic or aëriform state.
 2. Popular Usage (a) A complex mixture of gases, of which the most important constituents are marsh gas, olefiant gas, and hydrogen, artificially produced by the destructive distillation of gas coal, or sometimes of peat, wood, oil, resin, etc. It gives a brilliant light when burned, and is the common gas used for illuminating purposes. (b) Laughing gas. (c) Any irrespirable aëriform fluid.
 Note: ☞ Gas is often used adjectively or in combination; as, gas fitter or gasfitter; gas meter or gas-meter, etc.
 Air gas Chem., a kind of gas made by forcing air through some volatile hydrocarbon, as the lighter petroleums. The air is so saturated with combustible vapor as to be a convenient illuminating and heating agent.
 Gas battery Elec., a form of voltaic battery, in which gases, especially hydrogen and oxygen, are the active agents.
 Gas carbon, Gas coke, etc. See under Carbon, Coke, etc.
 Gas coal, a bituminous or hydrogenous coal yielding a high percentage of volatile matters, and therefore available for the manufacture of illuminating gas. --R. W. Raymond.
 Gas engine, an engine in which the motion of the piston is produced by the combustion or sudden production or expansion of gas; -- especially, an engine in which an explosive mixture of gas and air is forced into the working cylinder and ignited there by a gas flame or an electric spark.
 Gas fitter, one who lays pipes and puts up fixtures for gas.
 Gas fitting. (a) The occupation of a gas fitter. (b) pl. The appliances needed for the introduction of gas into a building, as meters, pipes, burners, etc.
 Gas fixture, a device for conveying illuminating or combustible gas from the pipe to the gas-burner, consisting of an appendage of cast, wrought, or drawn metal, with tubes upon which the burners, keys, etc., are adjusted.
 Gas generator, an apparatus in which gas is evolved; as: (a) a retort in which volatile hydrocarbons are evolved by heat; (b) a machine in which air is saturated with the vapor of liquid hydrocarbon; a carburetor; (c) a machine for the production of carbonic acid gas, for aërating water, bread, etc. --Knight.
 Gas jet, a flame of illuminating gas.
 Gas machine, an apparatus for carbureting air for use as illuminating gas.
 Gas meter, an instrument for recording the quantity of gas consumed in a given time, at a particular place.
 Gas retort, a retort which contains the coal and other materials, and in which the gas is generated, in the manufacture of gas.
 Gas stove, a stove for cooking or other purposes, heated by gas.
 Gas tar, coal tar.
 Gas trap, a drain trap; a sewer trap. See 4th Trap, 5.
 Gas washer Gas Works, an apparatus within which gas from the condenser is brought in contact with a falling stream of water, to precipitate the tar remaining in it. --Knight.
 Gas water, water through which gas has been passed for purification; -- called also gas liquor and ammoniacal water, and used for the manufacture of sal ammoniac, carbonate of ammonia, and Prussian blue. --Tomlinson.
 Gas well, a deep boring, from which natural gas is discharged. --Raymond.
 Gas works, a manufactory of gas, with all the machinery and appurtenances; a place where gas is generated for lighting cities.
 Laughing gas. See under Laughing.
 Marsh gas Chem., a light, combustible, gaseous hydrocarbon, CH4, produced artificially by the dry distillation of many organic substances, and occurring as a natural product of decomposition in stagnant pools, whence its name. It is an abundant ingredient of ordinary illuminating gas, and is the first member of the paraffin series. Called also methane, and in coal mines, fire damp.
 Natural gas, gas obtained from wells, etc., in Pennsylvania, Ohio, and elsewhere, and largely used for fuel and illuminating purposes. It is chiefly derived from the Coal Measures.
 Olefiant gas Chem.. See Ethylene.
 Water gas Chem., a kind of gas made by forcing steam over glowing coals, whereby there results a mixture of hydrogen and carbon monoxide. This gives a gas of intense heating power, but destitute of light-giving properties, and which is charged by passing through some volatile hydrocarbon, as gasoline.

From: WordNet (r) 2.0

 natural gas
      n : a fossil fuel in the gaseous state; used for cooking and
          heating homes [syn: gas]