Fossa, from the Latin fossa, ditch or trench.

Anatomically, a fossa is a depression or hollow. It is the most commonly used descriptive term in anatomy, seen in 64 different structures in the Terminologia Anatomica; the most frequently cited structure (on the Internet at least) is the iliac fossa, followed by the popliteal fossa, fossa ovalis, mandibular fossa, and olecranon fossa.

A word that shares Latin roots with fossa is fossil, coming from the Latin fossalis, dug up. Fossa and fossil ultimately stem from the Latin verb fodera, to dig.