Belly bad with churning — sign of things to come? (7)
I believe the answer is:
abdomen
'belly' is the definition.
(synonyms)
'bad with churning sign of things to come?' is the wordplay.
'with churning' is an anagram indicator (letters get churned around).
'sign of things to come?' becomes 'omen' (an omen is a sign of future events).
'bad' with letters rearranged gives 'abd'.
'abd'+'omen'='ABDOMEN'
(Other definitions for abdomen that I've seen before include "A main part of the body" , "guts" , "Part of body containing the stomach" , "Site of corporation" , "pot" .)