gambit

In chess, a gambit is an opening in which you give up a piece, usually a pawn, to gain position or speed. The queen's gambit, accept the gambit, decline the gambit.

The sacrifice is the point: an opening without one is not a gambit, however aggressive. A gambit can be accepted or declined, and both are named lines. In general use it means any opening move calculated to gain advantage: an opening gambit in a negotiation. Note that the everyday sense has lost the sacrifice entirely, which chess players find irritating and which is now thoroughly standard.