Posh MBA keeps rupees in dark place (5)
I believe the answer is:
umbra
'dark place' is the definition.
(I've seen this before)
'posh mba keeps rupees' is the wordplay.
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-U).
'keeps' indicates putting letters inside.
'rupees' becomes 'r' (abbreviation for rupees).
'mba' placed around 'r' is 'mbra'.
'u'+'mbra'='UMBRA'
'in' acts as a link.
(Other definitions for umbra that I've seen before include "Shadow's inner region" , "Region of shadow" , "shady region" , "Shade, or ghost" , "Black spot" .)