The British one, with which mum's out of practice? (6)
I believe the answer is:
museum
'the british one' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'mum's out of practice?' is the wordplay.
'out of' is an insertion indicator (some letters on the outside of others).
'practice?' becomes 'use' (practice is a kind of use).
'mum' enclosing 'use' is 'MUSEUM'.
'with which' acts as a link.
Can you help me to learn more?
(Other definitions for museum that I've seen before include "depository for historical objects" , "Repository for items of historical interest" , "Gallery of curiosities" , "Store of historical objects" , "tourist attraction" .)