Severe, spartan (7)
I believe the answer is:
austere
I believe this clue is a double definition.
'severe' is the first definition.
(I know that severe can be written as austere)
'spartan' is the second definition.
(I know that spartan can be written as austere)
(Other definitions for austere that I've seen before include "Without luxury or ornament" , "Severe, lacking comforts" , "Lacking comforts; strict" , "Severe; lacking luxuries" , "'Spartan, simple (7)'" .)