Quad'ru·plex adjective [ Latin , from quattuor four + plicare to fold.] Fourfold; folded or doubled twice. Quadruplex system (Electric Telegraph) , a system by which four messages, two in each direction, may be sent simultaneously over the wire. Found on http://www.encyclo.co.uk/webster/Q/3
fourfold; quadruple. · noting or pertaining to a system of telegraphy by which four messages may be transmitted simultaneously over one wire or communications channel. Found on https://www.infoplease.com/dictionary/quadruplex