Not happy with name of bird (7)
I believe the answer is:
bittern
'bird' is the definition.
(bittern is a kind of bird)
'not happy with name' is the wordplay.
I cannot really understand how this works, but
'name' could be 'n' (common abbreviation e.g. on forms) and 'n' is found in the answer.
The remaining letters 'bitter' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'of' is the link.
Can you help me to learn more?
(Other definitions for bittern that I've seen before include "Source of boom" , "Bird with a booming cry" , "''He shall not hear the ... cry / In the wild sky where he is lain'' (Lament for Thomas MacDonagh)" , "flier" , "Bird that booms" .)