Shortly the setter's retiring - one won't reveal his identity (6)
I believe the answer is:
anonym
'one won't reveal his identity' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'shortly the setter's retiring' is the wordplay.
'shortly' becomes 'anon' (synonyms).
'the setter's' becomes 'my' (belonging to the crossword setter).
'retiring' is a reversal indicator.
'my' written backwards gives 'ym'.
'anon'+'ym'='ANONYM'
Can you help me to learn more?
(Other definitions for anonym that I've seen before include "Unnamed publication or person" , "Fictitious name" , "Pseudonym" , "One whose name is not given" , "Person whose name is not given" .)