It can swell a father's pride (3)
I believe the answer is:
cub
This clue might be a double definition.
'it' is the first definition.
The definition suggests a singular noun which matches the answer.
'swell a father's pride' is the second definition.
The definition and answer can be both people as well as being singular nouns.
Maybe there's a link between them I don't understand?
'can' acts as a link.
Can you help me to learn more?
(Other definitions for cub that I've seen before include "Young lion or fox" , "Inexperienced reporter" , "Young bear or lion" , "Whelp" , "Baby animal, bear say" .)