Mystery writer, for short? (4)
I believe the answer is:
anon
'mystery writer for short?' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for anon that I've seen before include "before long" , "Shortly; unknown" , "Of unknown name (abbr)" , "Mystery writer" , "Presently - unattributed" .)