'blacken' originates from English, specifically the adjective 'black' combined with the verb-forming suffix '-en', where 'black' meant 'dark in color' and '-en' meant 'to make or become'.

'black' comes from Old English 'blæc' (meaning 'black, dark'); the verb-forming suffix '-en' (from Old English '-ian'/'-en') produced Middle English 'blaken'/'blacken', which evolved into the modern English 'blacken'.

Initially, it meant 'to make black or dark in color'; over time it retained that primary physical sense and also developed a figurative sense meaning 'to sully or tarnish (a reputation)'.