Posh philosopher finds employment (5)
I believe the answer is:
usage
'employment' is the definition.
(I know that employment can be written as usage)
'posh philosopher' is the wordplay.
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-U).
'philosopher' becomes 'sage' (sage can mean a wise person).
'u'+'sage'='USAGE'
'finds' is the link.
(Other definitions for usage that I've seen before include "Tradition - rate of consumption" , "Custom - treatment" , "Convention" , "Silly little thing" , "Habitual custom" .)