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. The meaning "active exertion, activity" is from late 14c. The sense of "something done, an act, deed" is late 14c. The meaning "military fighting" is from 1590s. The 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 attested 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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party (n.)

c. 1300, partie, "a part, division, section, portion," a sense now obsolete; also "physical piece, fragment; section of a book or treatise," from Old French partie "side, part; portion, share; separation, division" (12c.), literally "that which is divided," noun use of fem. past participle of partir "to divide, separate" (10c.), from Latin partire/partiri "to share, part, distribute, divide," from pars "a part, piece, a share" (from PIE root *pere- (2) "to grant, allot").

In early use the word often appears where we would have its relative part (n.). Also from c. 1300 in the legal sense "person or group of persons involved in a lawsuit, agreement, etc.," and in the political sense of "a number of persons united in supporting a person, policy, or cause." From early 14c. as any "group of people," also "a social class." Meaning "a person, a paritcular person" is from mid-15c.

The military sense of "a detached part of a larger body or company" is by 1640s. The sense of "a gathering for social pleasure" is found by 1716, from general sense of persons gathered (originally for some specific, temporary purpose, such as dinner party, hunting party).

Phrase the party is over "enjoyment or pleasant times have come to an end" is from 1937; party line is recorded by 1834 in the sense of "policy adopted by a political party," and by 1893 in the sense of "telephone line shared by two or more subscribers." Party pooper "one who casts gloom over a convivial event" is from 1951, American English.

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party (v.)

"have a good time," 1922, from party (n.). Earlier as "to take the side of" (1630s). Related: Partied; partying.

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tea party (n.)

1772, from tea + party (n.). Political references to tea party all trace to the Boston tea party of 1773 (the name seems to date from 1824), in which radicals in Massachusetts colony boarded British ships carrying tea and threw the product into Boston Harbor in protest against the home government's taxation policies. It has been a model for libertarian political actions in the U.S. (generally symbolic), including citizen gatherings begun in early 2009 to protest government spending.

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versus (prep.)

mid-15c., in legal case names, denoting action of one party against another, from Latin versus "turned toward or against," past participle of vertere "to turn," from PIE *wert- "to turn, wind," from root *wer- (2) "to turn, bend."

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defection (n.)

1540s, "action of failing," especially in performance of duty or obligation; 1550s, "action of deserting or abandoning a party, leader, cause, etc." (in early use often of faith); from Latin defectionem (nominative defectio) "desertion, revolt, failure," noun of action from past-participle stem of deficere "to desert, revolt, fail," from de "down, away" (see de-) + combining form of facere "to do, make" (from PIE root *dhe- "to set, put").

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know-nothing (n.)

1827, "ignoramus," from know (v.) + nothing. As a U.S. nativist political party, active 1853-56, the name refers to the secret society at the core of the party, about which members were instructed to answer, if asked about it, that they "know nothing." The party eventually merged into the Republican Party. Related: Know-nothingism.

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prosecution (n.)

1560s, "the carrying out or following up of anything" (also literal, "action of pursuing, a following after," but this is obsolete), from French prosecution (late 13c.) and directly from Late Latin prosecutionem (nominative prosecutio) "a following," noun of action from past-participle stem of prosequi "to follow after; chase, pursue; attack, assail" (see prosecute). The meaning "legal action, the institution and carrying out of a suit at law" is from 1630s. Hence, transferred, "the party by whom legal proceedings are initiated" (1891).

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allegation (n.)

early 15c., "action of alleging, formal declaration in court," from Old French alegacion "allegation, affirmation" (Modern French allégation) and directly from Latin allegationem (nominative allegatio) "a sending, dispatching," noun of action from past-participle stem of allegare "send for, bring forth, name, produce in evidence, send on business" (see allege). Specifically in law, "assertion of a party to a suit or action, which he intends to prove." In general (non-legal) use, since 17c., often suggesting an assertion without proof.

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