'assentient' originates from Latin, specifically the Late Latin present participle 'assentiens' from 'assentire', where the prefix 'ad-' (assimilated to 'as-') meant 'to/toward' and 'sentire' meant 'to feel, perceive'.

'assentire' (Latin) produced the participle 'assentiens' in Late Latin; this form came into English (via learned borrowing) as 'assentient' maintaining the sense of 'one who assents' or 'agreeing'.

Initially, it meant 'feeling toward or agreeing' in the literal Latin participial sense; over time it narrowed in English to mean 'giving assent' or 'one who assents'.