'attest' originates from Latin, specifically the word 'attestari', where 'ad-' meant 'to/toward' and 'testari' meant 'to bear witness (to testify).'.

'attestari' passed into Late Latin/Medieval Latin and Old French as words like 'attester' and entered Middle English as 'attesten' or 'attest', eventually becoming the modern English 'attest'.

Initially it meant 'to bear witness or testify', and over time it evolved into its current usage of 'to declare, certify, or provide evidence that something is true or genuine', a meaning that remains close to the original sense.