Debut of Gordon Fish, the writer (4)
I believe the answer is:
gide
'the writer' is the definition.
(author Andre Gide)
'debut of gordon fish' is the wordplay.
'debut of' indicates taking the first letters (I've seen 'debut' mean this).
'fish' becomes 'ide' (I've seen this in another clue).
The initial letter of 'gordon' is 'g'.
'g'+'ide'='GIDE'
(Other definitions for gide that I've seen before include "Andre --, French writer" , "Andre -, French novelist" , "Andre -, Fr. novelist" , "Andre -, C Nineteen-twenty French author" .)