A piano in small room is used by a star (7)
I believe the answer is:
capella
'star' is the definition.
(Capella is an example)
'a piano in small room is used by a' is the wordplay.
'piano' becomes 'p' (**).
'in' means one lot of letters goes inside another.
'small room' becomes 'cell' (I've seen this before).
'is used by' is a charade indicator (letters next to each other).
'a'+'p'='ap'
'ap' placed into 'cell' is 'capell'.
'capell'+'a'='CAPELLA'
(Other definitions for capella that I've seen before include "First-magnitude star" , "One of the brighest stars" , "Star in Auriga; Laplace (anag.)" .)