Butyrum, butyri, penult. interdum prod. interdum corr. Plin. Butter.
Lewis and Short: Latin dictionary
būtrum (, Sid. Carm. 12, 7; bŭ-tron, Aen. Mac. Herb. c. de ruta. buturum, Edict. Diocl. p. 15), i, n., = bou/turon [said to be a Scythian word, but prob. bou=sturo/s; Engl. butter],