Ace party? Shame! (5)
I believe the answer is:
abash
'shame' is the definition.
(I've seen this before)
'ace party?' is the wordplay.
'ace' becomes 'a'.
'party?' becomes 'bash' (bash is a kind of party**).
'a'+'bash'='ABASH'
(Other definitions for abash that I've seen before include "disgrace" , "put one to shame" , "Disconcert" , "Humiliate" , "Cause to feel ashamed" .)