Definition of ostium in English:


nounplural noun ostia/-tēə/

  • 1Anatomy Zoology
    An opening into a vessel or cavity of the body.

    ‘The latter arise from the paranasal sinuses and protrude into the nasopharynx through the sinus ostia.’
    • ‘An ascending dissection occasionally can occlude the ostium of a coronary artery and lead to myocardial infarction.’
    • ‘Accessory ostia of the maxillary sinus are found in about 30% of skulls; as many as three in one skull have been reported.’
    • ‘The location of the left-sided ostia of the lesions would be unusual for diverticula.’
    • ‘The ostium leads to the second portion of the oviduct, the ampulla, which is the duct's dilated mid-portion where fertilization usually occurs.’
    opening, orifice, aperture, hole, outlet, inlet, vent
    1. 1.1Zoology Each of a number of pores in the wall of a sponge, through which water is drawn in.
      ‘Water enters through pores called ostia, flows through canals to a spacious chamber called a spongocoel, and finally exits through large openings called oscula.’
      • ‘Both the sponges from Wyoming and those from the Great Basin have trabs of essentially the same size, as well as canals and ostia in the outer wall of essentially the same diameter.’
      • ‘For instance, many arthropods have lost extensive metamerism but still have remnants in the form of repeated organs (such as the limbs in cladocerans and spiders, or the heart ostia in a spider opisthosoma).’
      • ‘Brianispongia has numerous inhalant ostia or pores and scattered exhalant exopores, as in the Wyoming sponge.’
      • ‘Because of their lack of a continuous outer membrane and their lack of defined ostia, hexactinellids lack control over how much water passes through them.’



/ˈästēəm/ /ˈɑstiəm/


Early 17th century from Latin, ‘door, opening’.