Hypertext Webster Gateway: "Quadruplex"
From Webster's Revised Unabridged Dictionary (1913) (web1913)
Quadruplex \Quad"ru*plex\, a. [L., 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.
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