Spot material under piano (5)
I believe the answer is:
place
'spot' is the definition.
('place' can be a synonym of 'spot')
'material under piano' is the wordplay.
'material' becomes 'lace' (lace is a kind of material**).
'under' says to put letters next to each other.
'piano' becomes 'p'.
'lace' put after 'p' is 'PLACE'.
(Other definitions for place that I've seen before include "Scene; put" , "Put in - winning position" , "Venue" , "Endearingly pretty" , "square?" .)