'avouchable' ultimately originates from the verb 'avouch', which comes from Old French (e.g. 'avoucer'/'avoucher'), where the root is related to Latin elements such as 'ad-' (to/toward) and 'vocare' (to call).

'avouch' entered Middle English from Old French (Middle English forms include 'avouchen'/'avouchen'), and the adjective-forming suffix '-able' was later added in English to form 'avouchable'.

Initially the related words meant 'to call forward, acknowledge, or confess'; over time the sense shifted toward 'to assert or vouch for', and 'avouchable' developed the current meaning 'able to be affirmed or verified'.