'ancientest' is formed from the adjective 'ancient' with the superlative suffix '-est', following the pattern of English superlative formation.

'ancient' comes from Middle English 'auncien', from Old French 'ancien', from Latin 'anteanus', meaning 'former' or 'old'. The superlative 'ancientest' was formed in Early Modern English.

Initially, 'ancient' meant 'old' or 'from former times', and 'ancientest' simply meant 'most old'. This meaning has remained consistent, though 'ancientest' is now archaic and rarely used.