'accidentally-assisted' originates from English, specifically composed of the adverb 'accidentally' (from Latin 'accidens' / 'accidere', where 'ad-' meant 'to' and 'cadere' meant 'to fall' — giving a sense of 'that which happens') and the past participle 'assisted' (from Latin 'assistere' via Old French 'assister', where 'ad-' meant 'toward' and 'sistere' meant 'to stand').

'accidentally' developed from Latin 'accidens/accidere' into Anglo-Norman and Middle English forms (e.g. Middle English 'accident'), then formed the adverb 'accidentally'; 'assist' came from Latin 'assistere' → Old French 'assister' → Middle English 'assisten' → modern English 'assist', with the past participle 'assisted'. The compound adjective/phrase 'accidentally-assisted' is a modern English combination of these elements.

Initially, 'accidentally' meant 'by chance' and 'assist' originally meant 'to stand by or help'; over time the combined form came to mean 'help given unintentionally' or 'affected by unintended assistance'.