underbelly Syllabification: (un·der·bel·ly)Pronunciation: /ˈəndərˌbelē/Definition of underbelly noun (plural underbellies) the soft underside or abdomen of an animal. an area vulnerable to attack:these multinationals have a soft underbelly a hidden unpleasant or criminal part of society. underbelly in other Oxford dictionaries Definition of underbelly in the British & World English dictionary