A stout stem (7)
I believe the answer is:
staunch
I believe this is a double definition.
'a stout' 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 "Hearty" , "Arrest" , "Faithful and true" , "Trustworthy" , "Sturdy" .)