Small and friendly crowd (5)
I believe the answer is:
swarm
'crowd' is the definition.
(swarming is a kind of crowding)
'small and friendly' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'and' says to put letters next to each other.
'friendly' becomes 'warm' ('warm' can be a synonym of 'friendly').
's'+'warm'='SWARM'
(Other definitions for swarm that I've seen before include "Horde" , "Mob" , "Body of bees" , "Go to form new colony" , "Congregate" .)