Joint language as well as jazzy rhythm (6-3-6)
I believe the answer is:
tongue-and-groove
'joint' is the definition.
(tongue and groove joint is a kind of joint)
'language as well as jazzy rhythm' is the wordplay.
'language' becomes 'tongue' (tongue can mean a language).
'as well as' becomes 'and' (I've seen this in other clues).
'jazzy rhythm' becomes 'groove' (I can't explain this - if you can you should believe this answer much more).
'tongue'+'and'+'groove'='TONGUE-AND-GROOVE'
Can you help me to learn more?
(Another definition for tongue-and-groove that I've seen is " Board's joint".)