E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
The former is Norman, and the latter Saxon. The Normans had the cooked meat, and when set before them used the word they were accustomed to. The Saxon was the herdsman, and while the beast was under his charge called it by its Saxon name.
Old Alderman Ox continues to hold his Saxon title while he is under the charge of serfs and bondsmen; but becomes Beef, a flery French gallant, when he arrives before the worshipful jaws that are destined to consume him.Ivanhoe.
Weavers beef of Colchester, i.e. sprats, caught abundantly in the neighbourhood. (Fuller: Worthies.)