'grazer' ultimately comes from the verb 'graze' (Middle English 'grazen'), which is related to Old English 'grǣsan' meaning 'to eat grass' and from 'græs' meaning 'grass'.

'graze' developed from Old English 'grǣsan' and Middle English 'grazen'; the agent noun 'grazer' was formed in English by adding the suffix '-er' to denote 'one who grazes'. The modern plural form became 'grazers'.

Originally it meant 'to eat grass'; over time it came to refer both to the action of feeding on vegetation and to the animal that feeds that way (a 'grazer').