Shop piano, used in brooding genre, backing Mathieson? (8)
I believe the answer is:
emporium
'shop' is the definition.
(I have seen 'Large shop' mean 'emporium' so perhaps 'shop' could also mean 'emporium')
'piano used in brooding genre backing mathieson?' is the wordplay.
'piano' becomes 'p' (musical abbreviation).
'used in' is an insertion indicator.
'brooding genre' becomes 'emo' (I've seen this in another clue).
'backing' says the letters should be written backwards.
'mathieson?' becomes 'muir' (I can't explain this - if you can you should believe this answer much more).
'muir' backwards is 'rium'.
'p' going into 'emo' is 'empo'.
'empo'+'rium'='EMPORIUM'
Can you help me to learn more?
(Other definitions for emporium that I've seen before include "A large imposing shop" , "Big shop" , "Make up memoir about a very large shop" , "Large and ostentatious retail establishment" , "A large shop or centre of commerce" .)