Piano phrase messed up, maybe (7)
I believe the answer is:
perhaps
'maybe' is the definition.
(synonyms)
'piano phrase messed up' is the wordplay.
'piano' becomes 'p' (musical abbreviation).
'messed up' is an anagram indicator.
'phrase' anagrammed gives 'erhaps'.
'p'+'erhaps'='PERHAPS'
(Other definitions for perhaps that I've seen before include "Possibly but not certainly" , "say" , "Possibly, maybe" , "Not necessarily" , "Quite possibly" .)