Extremely rare swan with brown cygnet finally remorseful (9)
I believe the answer is:
repentant
'remorseful' is the definition.
('repentant' can be similar in meaning to 'remorseful')
'extremely rare swan with brown cygnet finally' is the wordplay.
'extremely' means to remove the middle letters.
'swan' becomes 'pen' (pen is a kind of swan).
'with brown' becomes 'tan' (tan is a kind of brown. I am not sure about the 'with' bit.**).
'finally' suggests the final letters.
'rare' with its middle taken out is 're'.
The final letter of 'cygnet' is 't'.
're'+'pen'+'tan'+'t'='REPENTANT'
Can you help me to learn more?
(Other definitions for repentant that I've seen before include "showing contrition" , "Feeling remorse for misdeeds" , "Contrite" , "Regretful" , "sorry state" .)