Omentum. The earliest recorded use of the word was by the Roman writer Celsus in the first century B.C. who referred specifically to the abdominal structure now called the greater omentum. The term has always been employed in an anatomical sense; there is no other known use.
Its derivation a mystery and Celsus left no clues. It may come from operimentum, Latin for the cloth used as a bed covering in ancient Rome much as the greater omentum covers the small intestine (the lesser omentum encloses the bile ducts and hepatic vessels). Others suggest it comes from opimus, Latin for plump, which would be an allusion to the fatty nature of the omenta. Or the term may come from the Latin omen, given the practice among some of the ancient soothsayers to prophesy using the entrails of sacrificed animals (and employing, as it were, a gut instinct as to what specific omens the visceral mess may signify).
The beer belly in men is due primarily to accumulation of greater omentum fat (with mesentery fat sometimes contributing). In women, abdominal fat is more likely to accumulate subcutaneously.