Firm, unyielding (5)
I believe the answer is:
stiff
This clue is a double definition.
'firm' is the first definition.
(I've seen this before)
'unyielding' is the second definition.
(I've seen this in another clue)
(Other definitions for stiff that I've seen before include "Difficult" , "Unfriendly" , "Unyielding" , "Awkward" , "Starched, rigid" .)