Army group in community (4)
I believe the answer is:
unit
'army group' is the definition.
(I've seen this before)
'in community' is the wordplay.
'in' indicates a hidden word.
'UNIT' is hidden within 'community'.
(Other definitions for unit that I've seen before include "army group" , "Single undivided entity" , "Individual thing; one" , "Single element; one" , "Specialised group" .)