Flyer in painfully cold north (7)
I believe the answer is:
bittern
'flyer in painfully cold north' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'cold north' is the wordplay.
'cold' becomes 'bitter' (similar in meaning).
'north' becomes 'N' (synonyms).
'bitter'+'n'='BITTERN'
Can you help me to learn more?
(Other definitions for bittern that I've seen before include "large wader" , "Source of boom" , "found hidden in reed-beds" , "Wading bird" , "'He shall not hear the . . . cry' (Ledwidge)" .)