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late 14c., "explanation, narration," from Old French esposicion (12c.), from Latin expositionem (nominative expositio) "a setting or showing forth," noun of action from past participle stem of exponere (see expound).
The meaning "public display" is first recorded 1851 in reference to the Crystal Palace Exposition in London. Abbreviation Expo is first recorded 1963, in reference to planning for the world's fair held in Montreal in 1967.