Natural inclination to be crooked (4)
I believe the answer is:
bent
I believe this is a double definition.
'natural inclination' is the first definition.
(I've seen this in another clue)
'be crooked' is the second definition.
(both can mean corrupt)
'to' is the link.
(Other definitions for bent that I've seen before include "Misshapen" , "Natural aptitude" , "Dodgy" , "passion" , "Personal inclination" .)