District initially summed up by "upmarket, rather bourgeois"? (6)
I believe the answer is:
suburb
'district' is the definition.
(suburb is a kind of district)
'initially summed up by upmarket rather bourgeois?' is the wordplay.
'initially' indicates taking the first letters.
The initial letters of 'summed up by upmarket rather bourgeois' is 'SUBURB'.
(Other definitions for suburb that I've seen before include "Residential urban district" , "Outer town area" , "Present (bill); melt down (fat)" , "Residential district away from city centre" , "District adjoining a town" .)