'hellish' originates from Old English, specifically the word 'hellisc', where 'hell' meant 'the underworld' and '-isc' was a suffix meaning 'of or pertaining to'.

'hellisc' transformed into the Middle English word 'hellish', and eventually became the modern English word 'hellish'.

Initially, it meant 'pertaining to hell', but over time it evolved into its current meaning of 'extremely unpleasant or difficult'.