embayment

Short definition from Wiktionary

Noun

1. 1
   A bay. (the water)
2. 2
   The shoreline of a bay, an indentation in a shoreline. (the land, not the water)
3. 3
   A topographical feature that used to be a bay, like the Mississippi embayment.
4. 4
   The process by which a bay is formed.