Definition of: duplex

(d′pleks, dy′-) adjective
1. Having two parts; double; twofold.
2. Having different faces, as some kinds of paper.
3. Mech. Working mechanically in two ways, whether in opposite directions along the same line, upon two things, by two similar parts, or by two separate operations at once.
4. Biol. Double, or with twice the number of parts; twinned.
—noun A duplex house or apartment. [<L <duo two + stem of plicare fold]
—du·plex′i·ty noun