'surly' originates from Middle English, specifically the word 'sirly' (from 'sir' + the adjectival suffix '-ly'), where the formation conveyed a 'lordly' or 'dominant' sense.

'surly' changed from Middle English 'sirly' (meaning 'lordly' or 'imperious') and, under folk etymology influences (including similarity to 'sour'), the form and senses shifted to the modern English 'surly'.

Initially, it meant 'lordly' or 'imperious', but over time it evolved into its current meaning of 'bad-tempered, rude, or unfriendly'.