Lachrymator (4,3)
I believe the answer is:
tear gas
'lachrymator' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for tear gas that I've seen before include "Crowd disperser" , "Used by police against rioters, irritates eyes" , "Riot control agent" , "Lacrimator" , "Riot controller" .)