Good person -- and a good party (4)
I believe the answer is:
stag
'party' is the definition.
(I've seen this before)
'good person and a good' is the wordplay.
'good person' becomes 'st' (saint).
'and' means one lot of letters go next to another.
'a good' becomes 'ag' (I've seen this in other clues).
'st'+'ag'='STAG'
(Other definitions for stag that I've seen before include "Unaccompanied man at party" , "One who speculates" , "Men-only" , "Antlered beast" , "Antlered animal" .)