ab·oma·sum .ab-ō-'mā-səm n, pl -sa -sə the fourth compartment of the ruminant stomach that follows the omasum and has a true digestive function compare RUMEN, RETICULUM
ab·oma·sal -səl adj
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ab·oma·sum (ab″o-maґsum) [ab- + L. omasum] the fourth stomach of a ruminant, comparable in structure and function to the stomach of a nonruminant; it contains gastric glands that secrete gastric juice. abomasal adjMedical dictionary. 2011.