I. ˈtri-ˌpleks, ˈtrī- noun
Date: 1571
: something (as an apartment) that is triplex
II. adjective
Etymology: Latin, from tri- + -plex -fold — more at -fold
Date: 1655
1. : threefold , triple
triplex windows
2. : having three apartments, floors, or sections
triplex buildings
triplex apartments
a triplex theater