One plated wing, garnished with a herb mayo base (9)
I believe the answer is:
armadillo
'one' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'plated wing garnished with a herb mayo base' is the wordplay.
I cannot really understand how this works, but
'wing' could be 'arm' (both can mean a side) and 'arm' is located in the answer.
'a' is within the answer.
'herb' could be 'dill' (dill is a kind of herb) and 'dill' is found in the answer.
A single letter 'o' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for armadillo that I've seen before include "protected species" , "Mammal with protective plates" , "Mammal covered with horny plates" , "Bony-plated insectivore" , "S. Am. plated mammal" .)