Unusually bad sign for the corporation (7)
I believe the answer is:
abdomen
'the corporation' is the definition.
(thesaurus)
'unusually bad sign' is the wordplay.
'unusually' indicates anagramming the letters.
'sign' becomes 'omen' (omen is a kind of sign).
'bad' anagrammed gives 'abd'.
'abd'+'omen'='ABDOMEN'
'for' acts as a link.
(Other definitions for abdomen that I've seen before include "gut" , "Midriff" , "Part of the body below chest and diaphragm" , "4 part of insect" , "A main part of the body" .)