Support for piano? (4)
I believe the answer is:
prop
'support' is the definition.
(prop up can mean to support)
'for piano' is the wordplay.
'for' becomes 'pro' (as in being 'pro' something).
'piano' becomes 'p' (musical abbreviation).
'pro'+'p'='PROP'
(Other definitions for prop that I've seen before include "Support (a rugby player?)" , "Seize and hold firmly" , "Support; object used on stage" , "player involved in scrum" , "Support; rugby forward" .)