'unarguably' is a modern English formation combining the negative prefix 'un-' with the adjective 'arguable' and the adverbial suffix '-ly'. 'Arguable' is derived from the verb 'argue'.

'argue' originates from Latin 'arguere' via Old French (e.g. 'arguer') into Middle English (e.g. 'arguen'/'arguen'), becoming English 'argue'; 'arguable' (adjective) was formed from 'argue' + '-able', then 'un-' was prefixed to form 'unarguable', and finally the adverbial suffix '-ly' produced 'unarguably'.

Originally from Latin 'arguere' meaning 'to make clear, to prove', the sense shifted in English to 'to present reasons' or 'to debate'; 'arguable' came to mean 'open to argument', so 'unarguable' meant 'not open to argument', and 'unarguably' now means 'in a manner that cannot reasonably be disputed'.