'asserve' originates from Latin, specifically the verb 'asseverare', where the prefix 'ad-/as-' meant 'to/toward' and the element related to 'severus' meant 'serious' (giving the sense 'to declare seriously/solemnly').

'asserve' changed from the Medieval Latin/Old French verb 'asseverer' and entered Middle English in forms such as 'assenver'/'asserven', eventually appearing as the rarer modern English form 'asserve'.

Initially, it meant 'to declare seriously or solemnly', but over time it evolved into its current (and now rare/archaic) meaning of 'to assert; to affirm'.