Jaw about musical work with a composer (6)
I believe the answer is:
chopin
'composer' is the definition.
(Frederic Chopin)
'jaw about musical work' is the wordplay.
'jaw' becomes 'chin' (I have seen 'Lower jaw' mean 'chin' so perhaps 'jaw' could also mean 'chin').
'about' means one lot of letters goes inside another.
'musical work' becomes 'op' (abbreviation for opus).
'chin' going around 'op' is 'CHOPIN'.
'with a' acts as a link.
(Other definitions for chopin that I've seen before include "Frederic . . . . . ., great Polish composer for piano" , "Double centenarian" , "Polish composer of much piano music" , "Romantic figure" , "Composer of "Tristesse"" .)