Duplex

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mid 16th century (as an adjective): from Latin duplex, duplic-, from duo ‘two’ + plicare ‘to fold’. The noun dates from the 1920s.

wiktionary

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Borrowed from Latin duplex(“double, two-fold”), from duo(“two”) + plico(“fold together”); compare πλέκω(plékō, “twist, braid”). Analyzable as duo- +‎ -plex.

etymonline

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duplex (adj.)

1817, "composed of two parts, double, twofold," from Latin duplex "twofold," from duo "two" (from PIE root *dwo- "two") + -plex, from PIE root *plek- "to plait." The noun in the sense of "house or other building so divided that it forms two dwelling places" (also sometimes "two-story apartment") is American English, by 1922.