Sinus Aestuum (Moon)

"Seething Bay"

Sinus Aestuum forms a northeastern extension to Mare Insularum. The eastern border is formed by an area of irregular terrain that divides the bay from the Mare Vaporum to the east. To the north is the Montes Apenninus range and the prominent crater Eratosthenes. (wikipedia entry)

A sinus is a small plain. On the Moon they are named after latin terms describing weather and other abstract concepts.