2 shut up (4)
I believe the answer is:
cage
This could be a double definition.
'2' is the first definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'shut up' is the second definition.
(I've seen this in other clues)
Can you help me to learn more?
(Other definitions for cage that I've seen before include "Coop" , "Pen" , "Prison (with bars)" , "he used to write down scores" , "Imprison, confine" .)