adj., n., & v.
adj. 1 exactly like something already existing; copied (esp. in large numbers). 2 a having two corresponding parts. b existing in two examples; paired. c twice as large or many; doubled.
n. 1 a one of two identical things, esp. a copy of an original. b one of two or more specimens of a thing exactly or almost identical. 2 Law a second copy of a letter or document. 3 (in full duplicate bridge or whist) a form of bridge or whist in which the same hands are played successively by different players. 4 archaic a pawnbroker's ticket.
v.tr. 1 multiply by two; double. 2 a make or be an exact copy of. b make or supply copies of (duplicated the leaflet for distribution). 3 repeat (an action etc.), esp. unnecessarily. duplicate ratio Math. the proportion of the squares of two numbers. in duplicate consisting of two exact copies. duplicable adj. duplication n.
[ L duplicatus past part. of duplicare (as DUPLEX) ]