Antisemitic affair victim ('Y') Freud treated with very little success (7)
I believe the answer is:
dreyfus
'antisemitic affair victim' is the definition.
(Alfred Dreyfus, victim in the Dreyfus affair)
'y freud treated with very little success' is the wordplay.
'treated with' indicates anagramming the letters.
'very little' says to take the initial letters.
The initial letter of 'success' is 's'.
'y'+'freud'='yfreud'
'yfreud' anagrammed with 's' makes 'DREYFUS'.
(Other definitions for dreyfus that I've seen before include "Frenchman involved in affair" , "French army officer" , "French captain, wrongly convicted 1894" , "The - Affair in France concerned a wrongly imprisoned officer" , "- Affair, in which Zola was involved" .)