[only before noun] made to look real, although it is actually a copy which does not work synonym replica a dummy bomb Word Origin late 16th cent.: from dumb + -y. The original sense was ‘a person who cannot speak’, then ‘an imaginary fourth player in whist’ (mid 18th cent.), whence ‘a substitute for the real thing’ and ‘a model of a human being’ (mid 19th cent.).