Group of musicians zip it at last (5)
I believe the answer is:
nonet
'group of musicians' is the definition.
(a nonet requires nine musicians)
'zip it at last' is the wordplay.
'zip' becomes 'none' (I've seen this in another clue).
'at last' says to take the final letters.
The last letter of 'it' is 't'.
'none'+'t'='NONET'
(Other definitions for nonet that I've seen before include "musical piece" , "Music for nine instruments or voices" , "Piece of music for nine" , "Piece for nine players" , "Work for nine players" .)