'sardonic' originates from Greek, specifically the word 'sardonikos', where 'sardo-' referred to Sardinia (and to a reputed local plant) and implied a bitter or convulsive grin.

'sardonic' changed from Latin 'sardonicus' and Old French 'sardonique' and eventually became the modern English word 'sardonic'.

Initially it meant 'a bitter or convulsive laughter/grin (associated with a plant from Sardinia)', but over time it evolved into its current meaning of 'grimly mocking or cynical'.