The Collaborative International Dictionary of English v.0.48:
belly up \bel"ly up`\, belly-up \bel"ly-up`\, a. [from analogy to the position of a floating dead fish.] defunct; bankrupt; -- used mostly of commercial organizations; often used in the phrase go belly-up, i. e. to go bankrupt. [PJC]WordNet (r) 3.0 (2006):
belly-up adj 1: financially ruined; "a bankrupt company"; "the company went belly-up" [syn: bankrupt, belly-up(p)]