Boy, a tense American, makes music (6)
I believe the answer is:
sonata
'music' is the definition.
(sonata is a kind of music)
'boy a tense american' is the wordplay.
'boy' becomes 'son' (synonyms).
'tense' becomes 't' (abbreviation used in many dictionaries).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'son'+'a'+'t'+'a'='SONATA'
'makes' acts as a link.
(Other definitions for sonata that I've seen before include "Piece of classical music" , "Musical piece" , "Classical composition" , "See 6" , "Chamber work" .)