'avower' ultimately derives from the verb 'avow' (Old French 'avouer'), which in turn comes from Latin roots; the Latin elements include 'ad-' meaning 'to/toward' and a root related to speaking or calling.

'avower' developed as the agent noun form of Middle English 'avowen' / Old French 'avouer' (to acknowledge or confess), producing the modern English noun 'avower' for 'one who avows'.

Originally linked to formally acknowledging or confessing (often in a legal or religious sense), the sense has remained close: someone who declares or admits openly.