Musical group without a safety measure (5)
I believe the answer is:
nonet
'musical group' is the definition.
(group of nine musicians)
'without a safety measure' is the wordplay.
'without' becomes 'no'.
'a safety measure' becomes 'net' (I've seen this in another clue).
'no'+'net'='NONET'
(Other definitions for nonet that I've seen before include "group composition" , "baseball team" , "Piece of music for nine" , "musical piece" , "Band's" .)