ˈästēəm noun
( plural os·tia -ēə)
Etymology: New Latin, from Latin, door, mouth of a river; akin to Russian ust'e mouth of a river, Sanskrit oṣṭha lip, Latin or-, os mouth — more at oral
: an entrance or opening: as
a. : either end of a Fallopian tube
b. : one of the lateral slits in the heart of an arthropod by which the blood enters from the pericardium