A duck retreats, nursing vulnerable wings (6)
I believe the answer is:
alevin
'a duck retreats nursing vulnerable wings' is the definition.
I can't judge whether this definition defines the answer.
'a duck retreats nursing vulnerable wings' is the wordplay.
'duck' becomes 'nil' (both can mean zero).
'retreats' shows that the letters should be reversed in order (I've seen 'retreat' mean this).
'nursing' indicates putting letters inside.
'vulnerable wings' becomes 'ev' (I can't justify this - if you can you should give a lot more credence to this answer).
'nil' backwards is 'lin'.
'lin' going around 'ev' is 'levin'.
'a'+'levin'='ALEVIN'
Can you help me to learn more?
(Other definitions for alevin that I've seen before include "Very fresh salmon" , "[FISH[" .)