'well-advised' originates from Modern English, composed of 'well' and the past participle 'advised'; 'well' ultimately comes from Old English 'wel' meaning 'in a good way', and 'advise' comes from Old French 'aviser' (see), where 'aviser' meant 'to consider or give counsel'.

'advise' entered English from Old French 'aviser' and developed into Middle English 'avisen'/'advisen'; the past participle 'advised' was used with 'well' to form the compound adjective 'well-advised' in Modern English.

Originally related to being 'given advice' or 'considered', the compound evolved into an adjectival sense meaning 'prudent' or 'sensible'.