Old English spæc "act of speaking; power of speaking; manner of speaking; statement, discourse, narrative, formal utterance; language," variant of spræc, from Proto-Germanic *sprek-, *spek- (source also of Danish sprog, Old Saxon spraca, Old Frisian spreke, Dutch spraak, Old High German sprahha, German Sprache "speech;" see speak (v.))
The spr- forms were extinct in English by 1200. Meaning "address delivered to an audience" first recorded 1580s.
And I honor the man who is willing to sink
Half his present repute for the freedom to think,
And, when he has thought, be his cause strong or weak,
Will risk t' other half for the freedom to speak,
Caring naught for what vengeance the mob has in store,
Let that mob be the upper ten thousand or lower.
[James Russell Lowell, "A Fable for Critics," 1848]
But when men have realized that time has upset many fighting faiths, they may come to believe even more than they believe the very foundations of their own conduct that the ultimate good desired is better reached by free trade in ideas — that the best test of truth is the power of the thought to get itself accepted in the competition of the market, and that truth is the only ground upon which their wishes safely can be carried out. That, at any rate, is the theory of our Constitution. It is an experiment, as all life is an experiment. ... I think that we should be eternally vigilant against attempts to check the expression of opinions that we loathe and believe to be fraught with death, unless they so imminently threaten immediate interference with the lawful and pressing purposes of the law that an immediate check is required to save the country. [Oliver Wendell Holmes Jr., dissent to "Abrams v. United States," 1919]
mid-15c., "to act upon or adjudicate" a legal case, from Latin actus, past participle of agere "to set in motion, drive, drive forward," hence "to do, perform," also "act on stage, play the part of; plead a cause at law" (from PIE root *ag- "to drive, draw out or forth, move").
Most of the modern senses in English probably are from the noun. General sense of "to do, perform, transact" is from c. 1600. Of things, "do something, exert energy or force," by 1751. In the theater from 1590s as "perform as an actor" (intransitive), 1610s as "represent by performance on the stage" (transitive). Meaning "perform specific duties or functions," often on a temporary basis, is by 1804.
To act on "exert influence on" is from 1810. To act up "be unruly" is by 1900 (in reference to a horse). Earlier it meant "acting in accordance with" a duty, expectation, or belief (1645). To act out "behave anti-socially" (1974) is from psychiatric sense of "expressing one's unconscious impulses or desires" (acting out is from 1945). Related: Acted; acting.
late 14c., "a thing done," from Latin actus "a doing; a driving, impulse, a setting in motion; a part in a play," and actum "a thing done" (originally a legal term), both from agere "to set in motion, drive, drive forward," hence "to do, perform," figuratively "incite to action; keep in movement, stir up," a verb with a broad range of meaning in Latin, including "act on stage, play the part of; plead a cause at law; chase; carry off, steal;" from PIE root *ag- "to drive, draw out or forth, move."
Theatrical ("part of a play," 1510s) and legislative (early 15c.) senses of the word also were in Latin. Meaning "one of a series of performances in a variety show" is from 1890. Meaning "display of exaggerated behavior" is from 1928, extended from the theatrical sense. In the act "in the process" is from 1590s, perhaps originally from late 16c. sense of the act as "sexual intercourse." Act of God "uncontrollable natural force" recorded by 1726.
An act of God is an accident which arises from a cause which operates without interference or aid from man (1 Pars. on Cont. 635); the loss arising wherefrom cannot be guarded against by the ordinary exertions of human skill and prudence so as to prevent its effect. [William Wait, "General Principles of the Law," Albany, 1879]
To get into the act "participate" is from 1947; to get (one's) act together "organize one's (disorderly) life" is by 1976.
"act in imitation of, imitate or copy in speech or action," 1680s, from mimic (n.). Related: Mimicked; mimicking.
early 14c., prologe, "introduction to a narrative or discourse," from Old French prologue (12c.) and directly from Latin prologus, from Greek prologos "preface to a play, speaker of a prologue," etymologically "a speech beforehand," from pro "before" (see pro-) + logos "discourse, speech," from legein "to speak," from PIE root *leg- (1) "to collect, gather," with derivatives meaning "to speak (to 'pick out words')." Especially a discourse or poem spoken before a dramatic performance or play. Figuratively, "a preliminary act or event," by 1590s.
early 15c., "act of communicating, act of imparting, discussing, debating, conferring," from Old French comunicacion (14c., Modern French communication) and directly from Latin communicationem (nominative communicatio) "a making common, imparting, communicating; a figure of speech," noun of action from past-participle stem of communicare "to share, divide out; communicate, impart, inform; join, unite, participate in," literally "to make common," related to communis "common, public, general" (see common (adj.)). Meaning "that which is communicated" is from late 15c.; meaning "means of communication" is from 1715. Related: Communications; communicational.