Ron's piano - possibly high-pitched? (9)
I believe the answer is:
sopranino
'high-pitched?' is the definition.
(similar in meaning)
'ron's piano possibly' is the wordplay.
'possibly' is an anagram indicator.
'rons'+'piano'='ronspiano'
'ronspiano' with letters rearranged gives 'SOPRANINO'.
(Other definitions for sopranino that I've seen before include "High-sounding instrument" , "higher instrument" .)