'attaint' originates from Old French, specifically the past-participle form 'ataint' (from verb 'ataindre'/'atendre'), ultimately from Vulgar Latin *attingere (from Latin components 'ad-' meaning 'to' and 'tingere'/'tangere' meaning 'to touch').

'attaint' entered Middle English from Anglo-Norman/Old French 'ataint' (past participle of 'ataindre'). The Old French forms (meaning 'reached' or 'touched') developed into English uses where the notion 'touched/affected' became 'tainted' or 'attainted' in legal contexts (leading to senses like 'stain' and 'convict').

Initially it meant 'reached' or 'touched' (literal sense); over time the sense shifted to 'affected' or 'tainted' and later was specialized in legal contexts to mean 'to declare guilty' or the state of 'attainder'.