'assentor' originates from Latin, specifically the word 'assentīre', where 'ad-' meant 'to' and 'sentīre' meant 'to feel or perceive'.

'assentor' changed from Old French/Anglo-Norman 'assenter' and Middle English forms (e.g. 'assentour'/'assenter') and eventually became the modern English word 'assentor'.

Initially it was tied to the verb sense 'to feel toward (agree)', but over time it evolved into the agent meaning 'one who gives assent' (a person who agrees).