ploy (ploi) n. An action calculated to frustrate an opponent or gain an advantage indirectly or deviously; a maneuver: "A typical ploy is to feign illness, procure medicine, then sell it on the black market"(Jill Smolowe).
1722, "anything with which one amuses oneself," Scottish and northern England dialect, possibly a shortened form of employ or deploy. Popularized in the sense "move or gambit made to gain advantage" by British humorist Stephen Potter (1900-1969).