ostentation n.

1730, "capable of being shown, that can be shown or seen, presentable," from French ostensible, from Latin ostens-, past-participle stem of ostendere "to show, expose to view; to stretch out, spread before; exhibit, display," from assimilated form of ob "in front of" (see ob-) + tendere "to stretch" (from PIE root *ten- "to stretch"). Meaning "apparent, professed, put forth or held out as real" is from 1771.

Ostensible is, literally, that may be or is held out as true, real, actual, or intended, but may or may not be so: thus, a person's ostensible motive for some action is the motive that appears to the observer, and is held out to him as the real motive, which it may or may not be. [Century Dictionary, 1895]

1701, "characterized by display or show from vanity or pride;" 1713, "showy, gaudy, intended for vain display," from ostentation + -ous. Earlier in a similar sense were ostentative (c. 1600); ostentive (1590s); ostentous (1620s). Related: Ostentatiously; ostentatiousness (1650s).