- a combining form meaning “having parts or units” of the number specified by the initial element, occurring originally in loanwords from Latin (duplex; quadruplex); recent English coinages ending in -plex, especially denoting structures with a given number of dwelling units, are probably in part new formations with this suffix and in part based on the noun complex: fourplex; eightplex; Cineplex; Metroplex.
Origin of -plex
< Latin -plex, -plic- (akin to plicāre to fold, bend, plectere to plait, braid; see -fold) + -s nominative singular ending
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
Word Origin and History for plex
in various usages, from Latin plex-, past participle stem of plectere "to plait" (see complex (adj.)).
Online Etymology Dictionary, © 2010 Douglas Harper