Stiff outfit I had (5)
I believe the answer is:
rigid
'stiff' is the definition.
(I know that stiff can be written as rigid)
'outfit i had' is the wordplay.
'outfit' becomes 'rig' (rigging is a kind of outfiting).
'i had' becomes 'i'd' (contraction).
'rig'+'id'='RIGID'
(Other definitions for rigid that I've seen before include "stern" , "completely" , "Not flexible" , "Unable to bend" , "Incapable of or resistant to bending" .)