Part of joint music group going north (5)
I believe the answer is:
tenon
'part of joint' is the definition.
(I've seen this in other clues)
'music group going north' is the wordplay.
'music group' becomes 'nonet' (group of nine musicians).
'going north' says the letters should be written in reverse.
'nonet' in reverse letter order is 'TENON'.
(Other definitions for tenon that I've seen before include "Wood fitting into a mortise" , "Part of wood joint" , "Shaped end of piece of wood for slotting into a hole." , "Kind of saw" , "Part of woodworking joint" .)