Lenient with him (7)
I believe the answer is:
clement
I believe this is a double definition.
'lenient' is the first definition.
('clement' can be similar in meaning to 'lenient')
'him' is the second definition.
'with' is the link.
(Other definitions for clement that I've seen before include "Mild or balmy" , "Patron saint of tanners" , "mercy" , "Of weather, mild and gentle" , "Kindly (applied to weather)" .)