Meaning

noun a house with two units sharing a common wall

noun an apartment having rooms on two floors that are connected by a staircase

verb change into a duplex

originPIE word *dwóh₁ Borrowed from Latin duplex (“double, two-fold”), from duo (“two”) + plico (“fold together”); compare the roots of διπλόος (diplóos, “double”); compare also πλέκω (plékō, “twist, braid”). By surface analysis, duo- + -plex.

Etymology from Wiktionary, CC BY-SA 3.0