Live ace? Not really for party (5)
I believe the answer is:
beano
'for party' is the definition.
(I've seen this before)
'live ace? not really' is the wordplay.
'live' becomes 'be' (synonyms).
'ace?' becomes 'a' (abbreviation).
'not really' becomes 'no'.
'be'+'a'+'no'='BEANO'
(Other definitions for beano that I've seen before include "A bone for a feast" , "Celebration" , "rowdy festivity" , "Informal party" , "Junket - children's comic" .)