In a way, weapons come in large numbers (6)
I believe the answer is:
swarms
'numbers' is the definition.
The definition and answer can be both groups as well as being plural nouns.
Maybe there's an association between them I don't understand?
'in a way weapons come in large' is the wordplay.
'in' means one lot of letters goes inside another.
'a way' becomes 's' (Compass direction - South).
'weapons' becomes 'arms' ('arm' can be a synonym of 'weapon').
'come in large' becomes 'w' (I can't explain this - if you can you should give a lot more credence to this answer).
's'+'arms'='sarms'
'sarms' enclosing 'w' is 'SWARMS'.
Can you help me to learn more?
(Other definitions for swarms that I've seen before include "Dense groups of flying insects" , "Large groups of flying bees" , "'Moving crowds, of bees say (6)'" .)