ostium

noun, plural os·ti·a [os-tee-uh] /ˈɒs ti ə/.

1. Anatomy, Zoology. a small opening or orifice, as at the end of the oviduct.
2. Zoology. one of the tiny holes in the body of a sponge.

noun plural -tia (-tɪə) biology

1. any of the pores in sponges through which water enters the body
2. any of the openings in the heart of an arthropod through which blood enters
3. any similar opening

n. pl. os•ti•a (-tē-ə)

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