Sit in the upper chamber (5)
I believe the answer is:
perch
'sit' is the definition.
(I know that perch is a more specific form of sit)
'in the upper chamber' is the wordplay.
'in' indicates the answer is hidden within the clue.
'PERCH' is hidden in the letters of 'upper chamber'.
(Other definitions for perch that I've seen before include "A fish; alighting place" , "Bird's seat - fish" , "(Fishy) pole where bird sits" , "bird comes down on" , "Settle" .)