Unbending, stiff (5)
I believe the answer is:
rigid
I believe this is a double definition.
'unbending' is the first definition.
(I know that unbending can be written as rigid)
'stiff' is the second definition.
(I know that stiff can be written as rigid)
(Other definitions for rigid that I've seen before include "Stiff and inflexible" , "Hard" , "Stiff, unmoving" , "unwilling to move" , "strict" .)