'oft-mentioned' is a compound formed from 'oft' and the past participle of 'mention'. 'oft' originates from Old English, specifically the word 'oft', where it meant 'often'; 'mention' originates from Old French, specifically the word 'mention', which comes from Latin 'mentio'.

'oft' remained largely unchanged from Old English 'oft' to modern English 'oft'; 'mention' changed from Latin 'mentio' to Old French 'mention' and Middle English 'mentioun', eventually becoming the modern English word 'mention'.

Initially the parts conveyed 'often' (from 'oft') and 'a calling to mind' (from 'mention'); combined as a phrase they originally implied 'often called to mind' and have come to mean 'frequently referred to' or 'mentioned frequently' in modern usage.