Room only for musician’s apparatus (5)
I believe the answer is:
cello
'musician's apparatus' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's a link between them I don't understand?
'room only' is the wordplay.
'room' becomes 'cell' (cell is a kind of room).
'only' becomes 'o' (this might be a standard abbreviation which I don't know about).
'cell'+'o'='CELLO'
'for' is the link.
Can you help me to learn more?
(Other definitions for cello that I've seen before include "Instrument in the violin family" , "music produced by this?" , "large-scale fiddle" , "Lloyd Webber's instrument" , "Casals' instrument" .)