oma·sum ō-'mā-səm n, pl oma·sa -sə the third chamber of the ruminant stomach that is situated between the reticulum and the abomasum called also manyplies, psalterium compare RUMEN
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oma·sum (o-maґsəm) [L.] the third stomach of a ruminant; its walls are lined with many folia that have rough surfaces, serving to grind up food. Called also manyplies and psalterium. omasal adjMedical dictionary. 2011.