ostia

/AA1 S T IY0 AH0/
noun
  1. 1

    A small opening or orifice, as in a body organ or passage.

  2. 2

    Any of the small openings or pores in a sponge.

  3. 3

    The mouth of a river.

Source: https://en.wiktionary.org/wiki/ostia, https://en.wiktionary.org/wiki/ostium