n.1 either of a pair of similar things, esp. either of two words of the same derivation but different sense (e.g. fashion and faction, cloak and clock).
2 hist. a man's short close-fitting jacket, with or without sleeves.
3 a historical or biblical account occurring twice in differing contexts, usu. traceable to different sources.
4 (in pl.) the same number on two dice thrown at once.
5 a pair of associated lines close together in a spectrum.
6 a combination of two simple lenses.
Etymology: ME f. OF f. double: see DOUBLE