Lewis & Short

†† ŏmāsum or ŏmassum, i, n. [Gallic; v. infra], bullock’s tripe (poet. and in post-Aug. prose): omasum βόειον κόπεον λιπαρὸν τῇ τῶν Τάλλων γλώττῃ, Gloss. Philox.: patinas cenabat omasi, Hor. Ep. 1, 15, 34; Plin. 8, 45, 70, § 180.
Transf.: pingui tentus omaso, with his fat paunch, Hor. S. 2, 5, 40.