Everything left ultimately to a Spartan serf (3,3)
I believe the answer is:
the lot
'everything' is the definition.
(thesaurus)
'left ultimately to a spartan serf' is the wordplay.
'ultimately' says to take the final letters.
'to a spartan serf' becomes 'helot' (I've seen this before).
The last letter of 'left' is 't'.
't'+'helot'='THE LOT'
(Other definitions for the lot that I've seen before include "Everything" , "goes under the hammer" .)