Lacrimator (4,3)
I believe the answer is:
tear gas
'lacrimator' is the definition.
(synonyms)
This is all the clue.
(Other definitions for tear gas that I've seen before include "Police weapon" , "Discharge sprayed by riot police" , "Volatile substance" , "Lacrimator" , "'It can be used to disperse crowds (4,3)'" .)