-plex

Having a given number of parts or units.

Latin plicare, to fold.

This ending can refer to numerical multiples: duplex, something having two parts; multiplex, consisting of many elements in a complex relationship; simplex (Latin, literally ‘single’, variant of simplus, simple), composed of or characterized by a single part or structure; googolplex, equivalent to ten raised to the power of a googol, itself an invented word meaning ten raised to the power of a hundred (10¹⁰⁰).

In addition, duplex can mean a residential building divided into two apartments, or two houses with a common wall (semi-detached in British usage), and a multiplex can be a cinema with several separate screens. This meaning, of a group of similar buildings or facilities on the same site, derives from one sense of complex, which comes from the same Latin stem.

Other examples—particularly common in North America—are triplex, a building divided into three self-contained residences; fourplex (also quadraplex and quadriplex), a building divided into four such residences; Cineplex, a trade name for a cinema with several separate screens; and, by extension, metroplex, a very large metropolitan area, especially one which is an aggregation of two or more cities. Several of these were originally blends (Cineplex from cinema and complex, for example), but ‑plex seems now to be established as a combining form in this sense.