Answer in song — answer that's a hateful thing (8)
I believe the answer is:
anathema
'a hateful thing' is the definition.
(I've seen this before)
'answer in song answer' is the wordplay.
'answer' becomes 'a' (abbreviation eg in Q and A).
'in' indicates putting letters inside.
'song' becomes 'anthem' (anthem is a kind of song).
'answer' becomes 'a' (abbreviation eg in Q and A).
'a' placed inside 'anthem' is 'anathem'.
'anathem'+'a'='ANATHEMA'
'that's' acts as a link.
(Other definitions for anathema that I've seen before include "Detested person or thing - excommunication" , "Cursed thing" , "One detested, cursed" , "Curse of the Church, or detested person" , "Condemned or excommunicated by church" .)