Ploy
late 17th century (originally Scots and northern English in the sense ‘pastime’): of unknown origin. The notion of ‘a calculated plan’ dates from the 1950s.
wiktionary
Possibly from a shortened form of employ or deploy. Or from earlier ploye, from Middle English, borrowed from Middle French ployer (compare modern plier), from Latin plicāre.
Probably abbreviated from deploy.
etymonline
ploy (n.)
1722, "anything with which one amuses oneself, a harmless frolic," Scottish and northern England dialect, possibly a shortened form of employ. Popularized 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."
