Building it's the custom to be silent going round (6)
I believe the answer is:
museum
'building' 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?
'the custom to be silent going round' is the wordplay.
'the custom' becomes 'use' (use is a kind of custom).
'to be silent' becomes 'mum' (keep mum).
'going round' is an insertion indicator (some letters go around others).
'use' put inside 'mum' is 'MUSEUM'.
'it's' acts as a link.
Can you help me to learn more?
(Other definitions for museum that I've seen before include "Building in which historical or scientific items are exhibited" , "Building for exhibition of historical objects" , "depository for historical objects" , "Place for exhibits of special interest" , "Building to display objects of historical interest" .)