A nickname is appropriate for him (8)
I believe the answer is:
nicholas
'him' is the definition.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for nicholas that I've seen before include "Russia's last emperor ..." , "Boy" , "Patron saint of Greece (and Liverpool)" , "Man's name; last tsar" , "Novel featuring Dotheboys Hall" .)