Gambit

gambit (n.)

"chess opening in which a pawn or piece is risked for advantage later," 1650s, gambett, from Italian gambetto, literally "a tripping up" (as a trick in wrestling), from gamba "leg," from Late Latin gamba "horse's hock or leg" (see gambol (n.)).

Applied to chess openings in Spanish in 1561 by Ruy Lopez, who traced it to the Italian word, but the form in Spanish generally was gambito, which led to French gambit, which has influenced the English spelling of the word. The broader sense of "opening move meant to gain advantage" in English is recorded from 1855.

also from 1650s

gambol (n.)

"frolic, merrymaking," 1590s, earlier gambolde "a skipping, a leap or spring" (1510s), from French gambade (15c.), from Late Latin gamba "horse's hock or leg," from Greek kampē "a bending;" see jamb. The form was altered perhaps by confusion with the formerly common ending -aud, -ald (as in ribald).

ploy (n.)

1722, "anything with which one amuses oneself, a harmless frolic," Scottish and northern England dialect, possibly a shortened form of employ. 

Popularised in the sense of "move or gambit made to manipulate others and gain advantage" by British humorist Stephen Potter (1900-1969), who parodied self-help manuals in books such as 1947's "The Theory and Practice of Gamesmanship : Or the Art of Winning Games Without Actually Cheating."

also from 1722

employ (v.)

early 15c., "apply or devote (something to some purpose); expend or spend," from Old French emploiier (12c.) "make use of, apply; increase; entangle; devote," from Latin implicare "enfold, involve, be connected with, unite, associate," from assimilated form of in- (from PIE root *en "in") + plicare "to fold" (from PIE root *plek- "to plait").

Imply, which is the same word, retains more of the original sense. Sense of "hire, engage" first recorded in English 1580s, from meaning "involve in a particular purpose," which arose in Late Latin. 

Related: Employed; employing; employable.