Equivalent to duo (“two”) + -plex (“-fold”). Possibly inherited from Proto-Italic *dupleks, if Umbrian 𐌕𐌖𐌐𐌋𐌀𐌊 (tuplak) is cognate (however, its meaning is uncertain and its form poses some difficulty). The Italic form may be an analogical alteration (with the du- of duo replacing *dwi-) of an original Proto-Indo-European *dwi-pleḱ-s; compare Ancient Greek δίπλαξ (díplax).