muttonhead, fool, idiotの略。後に雑種犬に対する罵倒語として使われる。
"That dog ain't no mutt," McManus would say as he stood behind the bar opening oysters; "no an he ain't no rube! Say! he's in it all the time when Charley trims the steaks." [Robert W. Chambers, "The Haunts of Men," 1898]Used by 1910 in dog fancier publications to refer to a non-purebred animal.