'arris' originates from Latin, specifically the word 'arista', where 'arista' meant 'awn, ear (of grain), or point'.

'arris' changed from Old French/Middle English forms derived from Latin 'arista' and eventually became the modern English word 'arris'.

Initially, it meant 'awn or point (as on a grain)', but over time it evolved into its current meaning of 'a sharp edge or ridge on masonry or moulding'.