Not entirely luxurious benefit (4)
I believe the answer is:
plus
'benefit' is the definition.
(thesaurus)
'not entirely luxurious' is the wordplay.
'not entirely' means to remove the last letter.
'luxurious' becomes 'plush' (I've seen this before).
'plush' with its last letter removed is 'PLUS'.
(Other definitions for plus that I've seen before include "To the French it's more" , "Positive thing" , "In addition, also" , "Something more" , "The opposite of minus" .)