embayment

noun

1. A bay. (the water)

   “The path climbed along a wall of purple sandstone above an embayment and in the sunlit shadows below him he could see the long cataphracted forms of gars lying in a kind of electric repose among the reeds.”

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