Group of three musicians (4)
I believe the answer is:
trio
'group of three musicians' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for trio that I've seen before include "A group or set of three" , "Piece for three players" , "Work for three" , "Beethoven's 'Archduke', for instance" , "Threesome" .)