Etymology
cooperate (v.)

also co-operate, "to act or operate jointly with another or others to the same end," c. 1600, from Late Latin cooperatus, past participle of cooperari "to work together with," from assimilated form of com "with, together" (see com-) + operari "to work," from PIE root *op- "to work, produce in abundance." Cooperator "fellow worker, associate" is attested from early 15c. Related: Cooperated; cooperating.

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*op- 

Proto-Indo-European root meaning "to work, produce in abundance."

It forms all or part of: cooperate; cooperation; copious; copy; cornucopia; hors d'oeuvre; inure; maneuver; manure; oeuvre; office; official; officinal; omni-; omnibus; omnium gatherum; op. cit.; opera; operate; operation; operose; optimism; optimum; opulence; opulent; opus; Oscan.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit apas- "work, religious act," apnas- "possession, property;" Hittite happina- "rich;" Avestan huapah- "doing good work, masterly;" Latin opus "a work, labor, exertion;" Greek ompne "food, corn;" Old High German uoben "to start work, to practice, to honor;" German üben "to exercise, practice;" Dutch oefenen, Old Norse æfa, Danish øve "to exercise, practice;" Old English æfnan "to perform, work, do," afol "power."

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non-cooperation (n.)

also noncooperation, "failure or refusal to cooperate," 1795, from non- + cooperation.

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synergetic (adj.)
"working together, cooperating," 1680s, from Greek synergetikos "cooperative," from synergein "to work together, cooperate" (see synergy). Synergic (1849) is from synergy + -ic.
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concord (v.)

late 14c., "reconcile, bring into harmony" (transitive); c. 1400, "agree, cooperate," from Old French concorder and directly from Latin concordare "be of one mind," from concors "of the same mind" (see concord (n.)). Related: Concorded; concording.

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collaborate (v.)
Origin and meaning of collaborate

1845 (implied in collaborating), "to work with another or others," a back-formation from collaborator or else modeled on French collaborer or directly from Late Latin collaboratus, past participle of collaborare. Given a bad sense in World War II: "Cooperate traitorously with an occupying enemy." Related: Collaborated.

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gung ho (adj.)

also gung-ho, gungho, 1942, slang motto of Carlson's Raiders (2nd Marine Raider Battalion, under Lt. Col. Evans Carlson, 1896-1947), U.S. guerrilla unit operating in the Pacific in World War II, from Chinese kung ho "work together, cooperate." Widely adopted in American English 1959.

Borrowing an idea from China, Carlson frequently has what he calls 'kung-hou' meetings .... Problems are threshed out and orders explained. [New York Times Magazine, Nov. 8, 1942]
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opportunist (n.)

1881, from opportunism (q.v.) + -ist. A word in Italian politics, later in France opportuniste was applied derisively to the moderate Léon Gambetta (1876), leader of the party between the monarchists and the extreme republicans. In English the word was used generally of anyone whose policy or tendency is to  seek to profit from the prevailing circumstances or take advantage of opportunities as they occur.

Once seated in the legislature Gambetta argued that all republicans—the old guard, young republicans, and even recent converts—could and should cooperate. He preached compromise and accommodation—Opportunism—in order to achieve the politically possible. He spoke against violent revolution and sought to promote peaceful reforms using legal methods, a stance that pitted him directly against the militant demagogue Henri Rochefort, who latched onto the term Opportunism as a term of abuse. [Robert Lynn Fuller, "The Origins of the French Nationalist Movement, 1886-1914"]
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play (v.)

Middle English pleien, from Old English plegan, plegian "move lightly and quickly, occupy or busy oneself, amuse oneself; engage in active exercise; frolic; engage in children's play; make sport of, mock; perform music," from Proto-West Germanic *plegōjanan "occupy oneself about" (source also of Old Saxon plegan "vouch for, take charge of," Old Frisian plega "tend to," Middle Dutch pleyen "to rejoice, be glad," German pflegen "take care of, cultivate"), which is apparently connected to the root of plight (v.), but the ultimate etymology is uncertain and the phonetic development is difficult to explain.

Meaning "to take part in" a martial or athletic game is from c. 1200. It has been opposed to work (v.) since late 14c. Meaning "perform or act on the stage" (transitive) is by late 14c., as are the senses of "take the role of" and "make a pretense of, make believe" and "act thoughtlessly or wantonly." Sense of "put forward, move, throw, lay on the table, etc." in the course of a game or contest is by 1560s of chess pieces, 1670s of playing cards. Sense of "operate or cause to operate with continuous or repeated action" is from 1590s. Meaning "to cause (a recording) to reproduce what is on it" is by 1903, probably from the "make music" sense. Related: Played; playing.

Many expressions are from the stage, sports and games, or music, and it is not always easy to say which is from which. To play up "emphasize" is from 1909 (perhaps originally "play music more vigorously"); to play down "minimize" is from 1930; to play along "pretend to agree or cooperate" is from 1929. To play fair "be nice" is from mid-15c. To play house as a children's activity is from 1958.

To play for keeps is from 1861, originally of marbles or other children's games with tokens. To play (something) safe is from 1911; to play favorites is attested from 1902.  To play second fiddle in the figurative sense is from 1809 ("Gil Blas"). To play into the hands (of someone) "act in such a way as to give the advantage to one's opponent or a third party" is from 1705. For play the _______ card see card (n.1). For play the field see field (n.). To play with oneself "masturbate" is from 1896 (to play with "have sexual intercourse with" is from mid-13c.). Playing-card "one of a pack of cards used for playing games" is from 1540s.

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