Etymology
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action (n.)

mid-14c., accioun, "cause or grounds for a lawsuit," from Anglo-French accioun, Old French accion, action (12c.) "action; lawsuit, case," from Latin actionem (nominative actio) "a putting in motion; a performing, a doing; public acts, official conduct; lawsuit, legal action" (source also of Spanish accion, Italian azione), noun of action from past-participle stem of agere "to do" (from PIE root *ag- "to drive, draw out or forth, move").

Spelling with the restored Latin -t- begins in 15c. Meaning "active exertion, activity" is from late 14c. Sense of "something done, an act, deed" is late 14c. Meaning "military fighting" is from 1590s. Meaning "way in which (a firearm, etc.) acts" is from 1845. As a film director's command, it is attested from 1923.

The meaning "noteworthy or important activity" in a modern sense by 1933, as in the figurative phrase a piece of the action (by 1965), perhaps from a sense of action in card-playing jargon by 1914.

No "action" can be had on a bet until the card bet upon appears. If it does not appear after a turn has been made, the player is at liberty to change his bet, or to remove it altogether. Each bet is made for the turn only, unless the player chooses to leave it until he gets some action on it. [from "Faro" in "Hoyle's Games," A.L. Burt Company, New York: 1914]

But there are uses of action as far back as c. 1600 that seem to mean "noteworthy activity." The meaning "excitement" is recorded from 1968. In action "in a condition of effective operation" is from 1650s. Phrase actions speak louder than words is attested from 1731. Action-packed is attested from 1953, originally of movies.

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natural (n.)

"person with a natural gift or talent," 1925, originally in prizefighting, from natural (adj.). But an older sense is almost opposite to this, "half-wit, idiot" (one "naturally deficient" in intellect), which was in use 16c. to 19c. In Middle English, the word as a noun meant "natural capacity, physical ability or power" (early 14c.), and it was common in sense "a native of a place" in Shakespeare's day. Also in 17c., "a mistress."

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natural (adj.)

c. 1300, naturel, "of one's inborn character; hereditary, innate, by birth or as if by birth;" early 14c. "of the world of nature (especially as opposed to man)," from Old French naturel "of nature, conforming to nature; by birth," and directly from Latin naturalis "by birth, according to nature," from natura "nature" (see nature).

Of events, features, etc., "existing in nature as a result of natural forces" (that is, not caused by accident, human agency, or divine intervention), late 14c. From late 14c. of properties, traits, qualities, "proper, suitable, appropriate to character or constitution;"  from late 15c. as "native, native-born." Also late 15c. as "not miraculous, in conformity with nature," hence "easy, free from affectation" (c. 1600). Of objects or substances, "not artificially cultivated or created, existing in nature" c. 1400. As a euphemism for "illegitimate, bastard" (of children), it is recorded from c. 1400, on the notion of blood kinship (but not legal status).

Natural science, that pertaining to physical nature, is from late 14c.;  natural history meaning more or less the same thing is from 1560s (see history).  Natural law "the expression of right reason or the dictate of religion inhering in nature and man and having ethically binding force as a rule of civil conduct" is from late 14c. Natural order "apparent order in nature" is from 1690s. Natural childbirth is attested by 1898. Natural life, usually in reference to the duration of life, is from mid-15c.; natural death, one without violence or accident, is from mid-15c. To die of natural causes is from 1570s.

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natural-born (adj.)

"so by nature, born so," 1580s, from natural (adj.) + born.

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naturalism (n.)

1630s, "action based on natural instincts," from natural (adj.) + -ism. In philosophy, as a view of the world and humanity's relationship to it involving natural forces only (and excluding spiritualism and superstition), from 1750. As a tendency in art and literature, "conformity to nature or reality, but without slavish fidelity to it," from 1850.

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naturalization (n.)

"act of naturalizing; state of being naturalized;" specifically in reference to the act of receiving an alien into the condition of a natural citizen, 1570s, from French naturalisation, noun of action from naturaliser (see naturalize).

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discoloration (n.)

1640s, "action of altering the natural or proper color of; condition of being discolored," noun of action from discolorate (early 15c.), from past-participle stem of Medieval Latin discolorare, from Latin dis- "off, away from" (see dis-) + colorare "to color," from color "color of the skin, color in general" (see color (n.)).

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naturality (n.)

early 15c., "natural character, quality of being natural, normality," from French naturalité, from Late Latin naturalitatem (nominative naturalitas), from Latin naturalis (see natural (adj.)). Meaning "natural feeling or conduct" is from 1620s.

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naturally (adv.)

late 13c., "inherently, intrinsically, characteristically," from natural (adj.) + -ly (2). From late 14c. as "in accord with natural law;" also "normally; usually, expectedly; as a matter of course, consequently, understandably." The notion is "as a natural result." From early 15c. as "without artificial assistance, by a natural process."

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physiology (n.)

1560s, "study and description of natural objects, natural philosophy" (a sense now obsolete), from French physiologie (16c.) or directly from Latin physiologia "natural science, study of nature," from Greek physiologia "natural science, inquiry into nature," from physios "nature" (see physio-) + logia "study" (see -logy). Meaning "science of the normal function of living things" is attested from 1610s. Related: Physiologic; physiologist.

The two words [physics/physiology] had once the same wide meaning of natural science or natural philosophy. They have now been narrowed & differentiated, physics retaining only the properties of matter & energy in inorganic nature, & physiology only the normal functions & phenomena of living beings. [Fowler, 1926]
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