Any additional item that follows a main work; (Theatre) an additional entertainment, spoken or sung, usually but not invariably comic, intended to…

a short opening piece performed before the principal play of the evening (cf. lever de rideau, n.); also transferred.

a performance, game, or (now chiefly) fight that takes place before the main event, esp. as the first event on the bill; a curtain-raiser; (also)…