Evil cardinal returning -- snake! (7)
I believe the answer is:
meander
'snake' is the definition.
(I've seen this in another clue)
'evil cardinal returning' is the wordplay.
'evil' becomes 'mean' (I can't justify this - if you can you should give a lot more credence to this answer).
'cardinal' becomes 'red' (I've seen this in another clue).
'returning' shows that the letters should be reversed in order.
'red' reversed gives 'der'.
'mean'+'der'='MEANDER'
Can you help me to learn more?
(Other definitions for meander that I've seen before include "Wander aimlessly like a stream" , "Red mane (anag) - roam aimlessly" , "Wind about or wander here and there" , "Wander about, follow a winding course" , "Take a winding course" .)