Evil demon put on feather - used to remain anonymous (3,2,5)
I believe the answer is:
nom de plume
'evil' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'demon put on feather used to remain anonymous' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'demon' is 'nomde' which is within the answer.
'feather' could be 'plume' (synonyms) and 'plume' is present in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for nom de plume that I've seen before include "Assumed name" , "George Sand?" , "False name" , "Pen-name" , "Author's pseudonym" .)