Lacks ability to show an inclination (4)
I believe the answer is:
cant
This clue is a double definition.
'lacks ability' is the first definition.
(I've seen this before)
'an inclination' is the second definition.
(I've seen this before)
'to show' acts as a link.
(Other definitions for cant that I've seen before include "Insincerity" , "'Language of a group, Travellers say (4)'" , "Hypocritical or sanctimonious talk" , "peculiar talk" , "Affected use of moral sentiments" .)