Definitions of belly:

• noun:   the underpart of the body of certain vertebrates such as snakes or fish
• noun:   a protruding abdomen
• noun:   the hollow inside of something

  Example: "In the belly of the ship"

• noun:   a part that bulges deeply

  Example: "The belly of a sail"

• noun:   the region of the body of a vertebrate between the thorax and the pelvis
• verb:   swell out or bulge out