early 18th century (as a verb): extension of express; express from express train, so named because it served a particular destination without intermediate stops, reflecting an earlier sense of express ‘done or made for a special purpose’, later interpreted in the sense ‘rapid’. Senses relating to express delivery date from the institution of this postal service in 1891.

late Middle English: from Old French expres, from Latin expressus ‘distinctly presented’, past participle of exprimere ‘press out’, from ex- ‘out’ + primere ‘press’.