Posh bishop and wife in eg New York underground (6)
I believe the answer is:
subway
'new york underground' is the definition.
(I've seen this before)
'posh bishop and wife in eg' is the wordplay.
'posh bishop' becomes 'ub' (I can't justify this - if you can you should give a lot more credence to this answer).
'and' says to put letters next to each other.
'wife' becomes 'w' (abbreviation).
'in' means one lot of letters goes inside another.
'eg' becomes 'say' (both can mean 'for example').
'ub'+'w'='ubw'
'ubw' put inside 'say' is 'SUBWAY'.
(Other definitions for subway that I've seen before include "Pedestrian way beneath a road" , "Pedestrian tunnel under a road" , "crossing point" , "NY underground" , "Pedestrian underpass" .)