Group is finally close to a discovery (5)
I believe the answer is:
swarm
'group' is the definition.
'is finally close to a discovery' is the wordplay.
'finally' suggests the final letters.
'close to a discovery' becomes 'warm' (someone getting warm is about to find something).
The final letter of 'is' is 's'.
's'+'warm'='SWARM'
(Other definitions for swarm that I've seen before include "Climb; cluster of bees" , "Army" , "Horde" , "Move in large numbers like locusts" , "Dense cloud (of insects)" .)