From Longman Dictionary of Contemporary Englishtear gastear gas /ˈtɪə ɡæs $ ˈtɪr-/ noun [uncountable] PMWa gas that stings your eyes, used by the police to control crowds The police used tear gas to break up the demonstration.
Examples from the Corpus
tear gas• A tear gas canister fatally wounded one young demonstrator.• The Army moved in with a water cannon and tear gas, forcing the marchers into hasty retreat.• Hundreds were hospitalized suffering from the effects of tear gas.• On Sept. 17 reports stated that tear gas was used to halt protests at a Mandalay high school.• They had to use tear gas to drive off the rioters.• Outside the group's headquarters, police and soldiers used tear gas against demonstrators.• The air was filled with tear gas and hordes of these balloons floating on to the streets below in the afternoon sun. 