Aged relative catches current number one's played in concert (5,5)
I believe the answer is:
grand piano
'aged relative' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'catches current number one's played in concert' is the wordplay.
I cannot quite see how this works, but
'current' could be 'i' (symbol for electric current) and 'i' is present in the answer.
'number' could be 'grand' (grand is a kind of number) and 'grand' is located in the answer.
'one' could be 'an' (an apple is one apple) and 'an' is found in the answer.
The remaining letters 'po' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for grand piano that I've seen before include "Large instrument with horizontal strings" , "Large stringed instrument" , "one getting tickled?" , "Keyboard instrument" , "responsible for producing notes ..." .)