Military; large number (4)
I believe the answer is:
army
I believe this clue is a double definition.
'military' is the first definition.
(the armed forces)
'large number' is the second definition.
(I've seen this in another clue)
(Other definitions for army that I've seen before include "Large number (of ants?)" , "Multitude" , "Large military body" , "Vast number" , "Throng" .)