Shepherd initially caring for flock (5)
I believe the answer is:
swarm
'flock' is the definition.
(thesaurus)
'shepherd initially caring' is the wordplay.
'initially' indicates taking the first letters.
'caring' becomes 'warm' (synonyms).
The first letter of 'shepherd' is 's'.
's'+'warm'='SWARM'
'for' acts as a link.
(Other definitions for swarm that I've seen before include "Flight of bees" , "Dense group (of insects)" , "Crowd of e.g. bees" , "Congregate" , "Large number" .)