an animal with long legs, that eats grass, leaves, etc. and can run fast. Most male deer have antlers (= horns shaped like branches). There are many types of deer. a herd of deer a deer park see also fallow deer, red deer, reindeer, roe deer, doe, fawn, stag See related entries: Wild mammals Word Origin Old English dēor, also originally denoting any four legged animal, used in the (now archaic) phrase small deer meaning ‘small creatures collectively’; of Germanic origin; related to Dutch dier, German Tier.