That whimsical fellow (3)
I believe the answer is:
'fellow' is the definition.
Both the answer and definition are singular nouns.
Perhaps you can see a link between them that I can't see?
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for him that I've seen before include "Objective male pronoun" , "Proper character" , "That man" .)