'assentor' originates from Latin, specifically the verb 'assentīre', where the prefix 'ad-' (appearing as 'as-') meant 'to/toward' and 'sentīre' meant 'to feel' or 'to perceive'.

'assentīre' passed into Medieval Latin/Old French as forms like 'assentare'/'assenter', entered Middle English as 'assenten' or 'assent', and the agent noun formed in English as 'assentor'.

Initially it related to 'feeling or showing agreement', and over time it came to mean specifically 'a person who gives approval or expresses agreement'.