Philosopher working for group of soldiers (7)
I believe the answer is:
platoon
'group of soldiers' is the definition.
(type of military subdivision)
'philosopher working' is the wordplay.
'philosopher' becomes 'plato' (Plato is an example).
'working' becomes 'on' (on can mean working or activated).
'plato'+'on'='PLATOON'
'for' acts as a link.
(Other definitions for platoon that I've seen before include "Team under lieutenant" , "Infantry unit" , "Sub-unit of a military company" , "Group of soldiers" , "Subdivision of a company" .)