Piano-key wood (5)
I believe the answer is:
ebony
'piano-key wood' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ebony that I've seen before include "Wood - Boyne (anag)" , "Very dark black" , "Heavy hard wood, usually black" , "Dark hardwood" , "'Hard, dark wood (5)'" .)