Duplex Du"plex, a. [L., fr. duo two + plicare to fold. See Two, and Complex.] Double; twofold. Duplex escapement, a peculiar kind of watch escapement, in which the scape-wheel has two sets of teeth. See Escapement. Duplex lathe, one for turning off, screwing, and surfacing, by means of two cutting tools, on opposite sides of the piece operated upon. Duplex pumping engine, a steam pump in which two steam cylinders are placed side by side, one operating the valves of the other. Duplex querela [L., double complaint] (Eccl. Law), a complaint in the nature of an appeal from the ordinary to his immediate superior, as from a bishop to an archbishop. --Mozley & W. Duplex telegraphy, a system of telegraphy for sending two messages over the same wire simultaneously. Duplex watch, one with a duplex escapement.