Inclination to be rotten (4)
I believe the answer is:
bent
I believe this is a double definition.
'inclination' is the first definition.
(bent is a kind of inclination)
'be rotten' is the second definition.
(thesaurus)
'to' acts as a link.
(Other definitions for bent that I've seen before include "Crooked - inclination" , "Crooked; grass" , "Misshapen" , "Special skill" , "Natural skill to be slangily dishonest?" .)