Definition of ostium in English:

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Pronunciation: /ˈästēəm/

noun (plural ostia /-tēə/)

Anatomy & Zoology
1An opening into a vessel or cavity of the body.
Example sentences
  • 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.
1.1 Zoology Each of a number of pores in the wall of a sponge, through which water is drawn in.
Example sentences
  • 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).


Early 17th century: from Latin, 'door, opening'.

For editors and proofreaders

Syllabification: os·ti·um

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