Late 16th century; earliest use found in Brian Melbancke (d. 1600), writer. As noun from post-classical Latin postmeridianum the hours after midday, afternoon, use as noun of neuter of classical Latin postmerīdiānus, adjective; as adjective from classical Latin postmerīdiānus (also in contracted form pōmerīdiānus) (adjective) of or occurring in the afternoon from post after + merīdiēs midday + -ānus. With use as adjective compare earlier pomeridian, and later antemeridian. With geological senses compare premeridian. In use as adverb perhaps erroneously for post meridiem.