Brit n.

U.S. colloquial shortening of Britisher or Briton, 1901, formerly (with Britisher) felt as offensive by Englishmen traveling in the States, who regarded it as another instance of the "odious vulgarism" of the Americans, but Bret and Bryt were common Old English words for the (Celtic) Britons and survived until c. 1300. In Old French, Bret as an adjective meant "British, Breton; cunning, crafty; simple-minded, stupid."