A firm tummy (11)
I believe the answer is:
corporation
I believe this is a double definition.
'a firm' is the first definition.
(I have seen 'Big firm' mean 'corporation' so perhaps 'firm' could also mean 'corporation')
'tummy' is the second definition.
('corporation' can be a synonym of 'tummy')
(Other definitions for corporation that I've seen before include "belly" , "target of 17, 8 [CHANCELLORS STATEMENT[" , "City body; paunch" , "Large firm" , "Stomach" .)