'unadvisable' originates from the prefix 'un-' meaning 'not' and the word 'advisable', which comes from the Latin 'advisare', meaning 'to consider'.

'advisare' transformed into the Old French word 'aviser', and eventually became the modern English word 'advise', with 'unadvisable' forming as a negation.

Initially, it meant 'not to be considered', and over time it evolved into its current meaning of 'not recommended or sensible'.