Fiercely loyal (7)
I believe the answer is:
staunch
'fiercely loyal' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for staunch that I've seen before include "Loyal; restrict (a flow of blood)" , "making it watertight" , "Very loyal, committed" , "Resolute" , "Reliable" .)