Unbending to equip one degree (5)
I believe the answer is:
rigid
'unbending' is the definition.
(I know that unbending can be written as rigid)
'equip one degree' is the wordplay.
'equip' becomes 'rig' (rigging is a kind of equiping).
'one' becomes 'i' (Roman numeral).
'degree' becomes 'd' (abbreviation for the degree in measuring angles).
'rig'+'i'+'d'='RIGID'
'to' is the link.
(Other definitions for rigid that I've seen before include "Unable to bend" , "Firmly fixed" , "not relaxing" , "Frozen" , "Stiff and inflexible" .)