'expressor' originates from Latin, specifically the word 'exprimere', where 'ex-' meant 'out' and 'primere' (from 'premere') meant 'to press'; the agentive suffix '-or' is from Latin, forming nouns meaning 'one who does X'.

'expressor' developed through Old French/Medieval Latin forms (e.g. Old French/Anglo-Norman forms from 'exprimer'/'exprimere') into Middle English (recorded as 'expressour'/'expressor') and eventually the modern English 'expressor'.

Initially associated with the literal sense 'to press out' (from Latin), it shifted to the figurative sense 'to convey or put into words/manifest', leading to the agent noun sense 'one who expresses' used today.