'blacken' originates from English, formed from the adjective 'black' + the verb-forming suffix '-en' (Old English/Germanic origin), where 'black' meant 'black, dark' and '-en' meant 'make or become'.

'black' comes from Old English 'blæc' meaning 'black, dark'; the verb was formed in Middle English as 'blackenen' and later became the modern English verb 'blacken'.

Initially it meant 'to make black or dark'; over time the core sense has remained, while figurative uses (e.g., to damage reputation) developed.