A party in trouble (3)
I believe the answer is:
ado
'trouble' is the definition.
(thesaurus)
'a party' is the wordplay.
'party' becomes 'do' (do is a kind of party).
'a'+'do'='ADO'
'in' acts as a link.
(Other definitions for ado that I've seen before include "Pother" , "Fuss, bother" , "Fuss or bustle" , "Shakespeare: 'Much ... About Nothing'(3) ()" , "Flap" .)