A gambit is the sacrifice of one thing in order to obtain something else, in a calculated risk. The Passion of Christ was the most significant gambit of all.
As applied to chess, it refers to losing pieces, usually a pawn or two, in order to obtain a strategic advantage. (There are some exceptions, such as the Muzio Gambit, which sacrifices an entire knight, or Bobby Fischer's famous queen's gambit.)
A gambit is also a small tool used to attach a cantle to a sporran.
Mike Gambit was a character in mid-70s British action series The New Avengers, played by coffee salesman Gareth Hunt (d.2007).
Increasingly the term gambit is used to refer to any calculated maneuver.