'assumer' originates from Latin, specifically the word 'assumere', where 'ad-' (often assimilated to 'as-') meant 'to' and 'sumere' meant 'to take'.

'assumere' passed into Old French as 'assumer' and into Middle English (as forms like 'assumen'), eventually producing the modern English verb 'assume' and the agent noun 'assumer' (and its plural 'assumers').

Initially it meant 'to take up' or 'to take to oneself' in a literal sense; over time it broadened to mean both 'to suppose' (to take something as true) and 'to take on' (responsibility), senses that persist today.