Cage bird (6)
I believe the answer is:
prison
This might be a double definition.
'cage' is the first definition.
(I've seen this in another clue)
'bird' is the second definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps there's a link between them I don't understand?
Can you help me to learn more?
(Other definitions for prison that I've seen before include "Place of incarceration" , "Place of confinement" , "Correctional institution" , "Stir - can" , "Place of detention for criminals" .)