The AHD notes that venison is:

1. The flesh of a deer used as food.

2. Archaic The flesh of a game animal used as food.

Etymologically speaking, venison entered Modern English by way of Middle English veneson, from Old French venetio, from Latin venatio, venation-, hunting, from venatus, past participle of venari, to hunt.

In England's middle ages in England, after William the Conqueror settled his Norman French supporters on English lands and estates during the Norman conquest of 1066 meant that the language of those in power switched, almost immediately, from Anglo-Saxon or Old English, to the Norman French of the conquerors. The conquering aristocrats, Williams knights and their supporters, spoke Norman French, and their English servants and the peasants Old English. Consequently the servant who dressed and butchered meat for his Norman lord called the animal deer, while once it was brought to the table, it was called venison. Sheep lived in the fields, but when butchered and prepared for the local aristocratic, feudal lord, the meat was transformed to mutton.

Initially venison was used, in both Norman French and English, to refer to not just deer, but any animal killed in the chase, or by hunters, and used as food (OED venison). With use, and time, venison began to refer exclusively to deer. The early history of venison is still preserved in its etymology. The word venison is cognate with venerate, venery, Venus, and venereal, all words descended from the Proto Indo-European root *-wen-1(AHD), "to desire or strive for." Consequently, puns on Venus, the goddess of love and desire, and venison, and venery, the art of the hunt, are frequent in both Latin and in English poetry, which uses metaphors of the deer hunt, for example, to discuss the hunt for love and sex.