adjective

1. double; twofold
2. designating or of a system of telegraphy in which two messages may be sent simultaneously in opposite directions over a single circuit
3. Machinery having two units operating in the same way or simultaneously

Etymology: L, consisting of two leaves, double < duo, two + -plex, -fold < plicare, to fold < IE base *plak-, *plag- > flag, Gr plax, surface, infl. by early assoc. with duplus, double

noun

1. duplex house
2. duplex apartment