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Ostium

/ˈästēəm/

Noun, pl. ostia

1. A small opening or orifice, as in a body organ or passage. (wiktionary.org)

2. a. Any of the small openings or pores in a sponge. (wiktionary.org)

b. Each of a number of pores in the wall of a sponge, through which water is drawn in. (Google Dictionary)

3. A mouthlike opening in a bodily part (as a fallopian tube or a blood vessel). (merriam-webster.com)