Fuss at a party (3)
I believe the answer is:
'fuss' is the definition.
'at a party' is the wordplay.
'at' means one lot of letters go next to another.
'party' becomes 'do' (do is a kind of party).
'a' put next to 'do' is 'ADO'.
(Other definitions for ado that I've seen before include "flapping" , "Fuss, trouble" , "Goings-on" , "Song and dance" , "hoo-hah" .)