'well-attested' originates from English, specifically a compound of 'well' and 'attested', where 'well' ultimately comes from Old English 'wel' and 'attested' derives from Latin 'attestari'.

'attestari' changed into Old French/Latin-influenced forms such as 'attester' and Middle English 'attesten', and combined with the adverb/adjective 'well' in Modern English to form the compound 'well-attested'.

Initially, 'attest' meant 'to bear witness' or 'give testimony'; over time 'attested' came to mean 'documented or confirmed', and 'well-attested' evolved to mean 'strongly or reliably supported by evidence'.