Side’s average, totally soulless (5)
I believe the answer is:
party
'side's' is the definition.
(thesaurus)
'average totally soulless' is the wordplay.
'average' becomes 'par' (average score in golf).
'totally soulless' becomes 'ty' (I can't explain this - if you can you should believe this answer much more).
'par'+'ty'='PARTY'
Can you help me to learn more?
(Other definitions for party that I've seen before include "Group gathered together for pleasure" , "festive" , "MP's faction" , "Festivity" , "Crew" .)