1. The front or under part of a vertebrate body from the breastbone to the pelvis, containing the abdominal viscera; the abdomen
2. Appetite or capacity for food; gluttony
3. The womb
4. The interior or inside of anything
Sooooo, belly comes from Old English belg ("leather bag, purse, bellows"), which derived from Proto-Germanic *balgiz ("bag") from Proto-Indo-European *bhel- ("to blow, swell"). The meaning of "body" didn't arise until the late 13th century, and by the mid-14th century it had shifted to mean "abdomen" specifically.