A small friendly throng (5)
I believe the answer is:
swarm
'throng' is the definition.
(I've seen this in another clue)
'a small friendly' is the wordplay.
'a small' becomes 's' (abbreviation - e.g. clothes size).
'friendly' becomes 'warm' (warm can mean friendly or affable).
's'+'warm'='SWARM'
(Other definitions for swarm that I've seen before include "Hive" , "New colonists" , "Arrive in numbers" , "Crowd of e.g. bees" , "Dense cloud (of insects)" .)