os externum
/ˌɒs ɪkˈstəːnəm/ /ˌɒs ɛkˈstəːnəm/Anatomy. Now rare
noun
Originally: †the external opening of the vagina (obsolete ). In later use: the opening of the cervix into the vagina; the os uteri.
Origin
Mid 18th century; earliest use found in William Smellie (1697–1763), man-midwife. From post-classical Latin os externum from classical Latin ōs + externum, neuter of externus outer.