Concert instrument that's flat (5,5)
I believe the answer is:
grand piano
This clue could be a double definition.
'concert instrument' is the first definition.
(I've seen this in another clue)
'flat' is the second definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for grand piano that I've seen before include "Large stringed instrument" , "Keyboard instrument" , "one getting tickled?" , "Large instrument with horizontal strings" , "responsible for producing notes ..." .)