Puck's choice of pseudonym in evidence (4)
I believe the answer is:
mine
'puck's choice' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'of pseudonym in evidence' is the wordplay.
'of' indicates the answer is hidden within the clue.
'MINE' is hidden within 'pseudonym in evidence'.
(Other definitions for mine that I've seen before include "An abundant source, as of gold" , "Bomb - colliery" , "Pit; source" , "Dig for minerals like coal" , "Coalpit" .)