Boy gets a “thank you” for piano piece perhaps (6)
I believe the answer is:
sonata
'piano piece perhaps' is the definition.
(a sonata might be played on piano)
'boy gets a thank you' is the wordplay.
'boy' becomes 'son' (synonyms).
'gets' says to put letters next to each other.
'thank you' becomes 'ta'.
'son'+'a'+'ta'='SONATA'
'for' is the link.
(Other definitions for sonata that I've seen before include "Solo instrumental composition" , "composition for piano, perhaps" , "Music to play (not sing)" , "Eg, Beethoven's Kreutzer or Spring" , "Beethoven's 'Moonlight', for example" .)