Smallish combo (4)
I believe the answer is:
trio
'smallish combo' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for trio that I've seen before include "Beethoven's 'Archduke': famous piece written for this ensemble" , "Musical group" , "Three of a kind" , "Three together" , "(Composition for) three performers" .)