'arrant' originates from Old French, specifically the word 'errant', where the root came from Latin 'errare' meaning 'to wander'.

'arrant' changed from Middle English 'arrant' (from Old French 'errant') and eventually became the modern English adjective 'arrant' (and by extension the adverb 'arrantly').

Initially it meant 'wandering' or 'straying' (from Latin 'errare'), but over time it evolved into the sense 'notorious' or 'complete' (as in 'arrant scoundrel').