Stiff, inflexible (5)
I believe the answer is:
rigid
This clue is a double definition.
'stiff' is the first definition.
(I know that stiff can be written as rigid)
'inflexible' is the second definition.
(I know that inflexible can be written as rigid)
(Other definitions for rigid that I've seen before include "completely" , "not relaxing" , "Not flexible" , "Stiff and inflexible" , "starched too much?" .)