Definition of omasum in English:


nounPlural omasa

  • The muscular third stomach of a ruminant animal, between the reticulum and the abomasum.

    Also called psalterium
    • ‘To do this they are doing experiments in small chambers, called parabiotic chambers, that use stomach tissue from sheep to simulate that of the rumen and the omasum, two of the four compartments in a cow's stomach.’
    • ‘The stomach of mouse deer is three chambered (lacking a well-developed omasum), and these animals are ruminants.’
    • ‘The reticulum is connected to the spherical omasum by a short tunnel.’
    • ‘By definition, foregut fermentors comprise animals with a pregastric fermentation chambers such as the rumen, reticulum, and omasum of ruminants and diverticula or fermentative sacs of other ruminant-like mammals.’
    • ‘The omasum is composed of numerous layers between which food is crushed.’


Early 18th century: from Latin, literally ‘bullock's tripe’.