Party before long for senior member (5)
I believe the answer is:
doyen
'for senior member' is the definition.
(a senior or respected figure)
'party before long' is the wordplay.
'party' becomes 'do' (do is a kind of party).
'before' says to put letters next to each other.
'long' becomes 'yen' (synonyms).
'do'+'yen'='DOYEN'
(Other definitions for doyen that I've seen before include "Respected senior member" , "Member greatly respected" , "Senior member of a professional group" , "Senior male figure in a profession" , "Man who is the senior in his profession" .)