Firm stem (7)
I believe the answer is:
staunch
This clue is a double definition.
'firm' is the first definition.
(thesaurus)
'stem' is the second definition.
('staunch' can be a synonym of 'stem')
(Other definitions for staunch that I've seen before include "Check" , "Trusty - steadfast" , "Loyal; restrict (a flow of blood)" , "Resolute" , "Firm in loyalty" .)