For the pianist, it can be sustaining (5)
I believe the answer is:
pedal
'for' is the definition.
Both the answer and definition are singular nouns.
Perhaps there's an association between them I don't understand?
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for pedal that I've seen before include "One may be sustaining" , "related to feet" , "sustained note" , "ride a cycle" , "Bicycle footrest" .)