Instrument Spike brought into group (6)
I believe the answer is:
spinet
'instrument' is the definition.
(spinet is a kind of instrument)
'spike brought into group' is the wordplay.
'spike' becomes 'pin' (pinning is a kind of spiking).
'brought into' is an insertion indicator.
'group' becomes 'set' (set is a kind of group).
'pin' inserted within 'set' is 'SPINET'.
(Other definitions for spinet that I've seen before include "organ" , "A small harpsichord of old" , "Early keyboard instrument" , "Step in with old harpsichord" , "Old keyboard instrument" .)