Sit in the upper chamber (5)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
perch
'sit' is the definition.
(perching is a kind of sitting)
'in the upper chamber' is the wordplay.
'in' indicates a hidden word.
'PERCH' can be found hidden inside '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" .)