Man's inheritance supports party, a brilliant gathering (6)
I believe the answer is:
galaxy
'a brilliant gathering' is the definition.
'galaxy' can be an answer for 'gathering' (galaxy is a kind of gathering). I am unsure of the 'a brilliant' bit.
'man's inheritance supports party' is the wordplay.
'man's inheritance' becomes 'xy' (I can't justify this - if you can you should believe this answer much more).
'supports' is a charade indicator (letters next to each other) (bottom letters provide a support for the top ones).
'party' becomes 'gala' (I've seen this before).
'xy' after 'gala' is 'GALAXY'.
Can you help me to learn more?
(Other definitions for galaxy that I've seen before include "Huge collection of stars" , "A lot of stars" , "Spiral, elliptical, group of stars" , "System of stars - assembly of talent" , "Astronomical system" .)