Cunning holding up piano store (6)
I believe the answer is:
supply
'store' is the definition.
(I've seen this before)
'cunning holding up piano' is the wordplay.
'cunning' becomes 'sly' (synonyms).
'holding' means one lot of letters goes inside another.
'piano' becomes 'p' (musical abbreviation).
'up'+'p'='upp'
'sly' going around 'upp' is 'SUPPLY'.
(Other definitions for supply that I've seen before include "store" , "Stand-in teacher" , "Furnish goods or services" , "Fund" , "Make available" .)