early 15c., "to leave without shelter or defense," from Middle French exposer "lay open, set forth" (13c.), from Latin exponere "set forth" (see expound), altered by confusion with poser "to place, lay down" (see pose (v.1)). Meaning "to exhibit openly" is from 1620s; that of "to unmask" is from 1690s. Photographic sense is from 1839. Related: Exposed; exposes; exposing.