Only cold dessert? Right! (7)
I believe the answer is:
justice
'right' is the definition.
(thesaurus)
'only cold dessert?' is the wordplay.
'only' becomes 'just' (synonyms).
'cold dessert?' becomes 'ice' (eg an ice lolly).
'just'+'ice'='JUSTICE'
(Other definitions for justice that I've seen before include "Equity" , "Rightness" , "One of man's 22 20 [SEVEN AGES]" , "Fairness, legitimacy" , "Magistrate's title" .)