Ensemble takes on posh place -- one of five (10)
I believe the answer is:
quintuplet
'one of five' is the definition.
(I've seen this in another clue)
'ensemble takes on posh place' is the wordplay.
'ensemble takes' becomes 'quintet' (I can't explain this - if you can you should give a lot more credence to this answer).
'on' is an insertion indicator (as in clothing 'on' a person).
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-U).
'place' becomes 'pl' (abbreviation used in postal addresses).
'u'+'pl'='upl'
'quintet' enclosing 'upl' is 'QUINTUPLET'.
Can you help me to learn more?
(Other definitions for quintuplet that I've seen before include "One of five born together" , "one of several children" , "One arriving in group" , "complicated delivery component" .)