Belly wobbling bad sign (7)
I believe the answer is:
abdomen
'belly' is the definition.
(synonyms)
'wobbling bad sign' is the wordplay.
'wobbling' is an anagram indicator.
'sign' becomes 'omen' (omen is a kind of sign).
'bad' with letters rearranged gives 'abd'.
'abd'+'omen'='ABDOMEN'
(Other definitions for abdomen that I've seen before include "Midriff" , "Region of the body between the thorax and pelvis" , "Belly" , "corporation's site" , "guts" .)