From Longman Dictionary of Contemporary Englishgun somebody ↔ down phrasal verbSHOOTto shoot someone and badly injure or kill them, especially someone who cannot defend themselves A policeman was gunned down as he left his house this morning.Grammar Gun down is usually passive. → gun→ See Verb table
Examples from the Corpus
gun down• Still, given our fondness for gunning each other down, fearing the sight of blood seems perfectly sound.• Use your pistol to dispense with individual guards or your machine gun to mow down a line of enemies.• The shrapnel and spent machine gun bullets pattered down among the cactus like rain.• The gun hangs down below the hem of her skirt.• It follows, of course, that each time a gun is laid down it must first be broken and unloaded.• The new ships will have two sets of rapid-fire radar-controlled multi-barrel guns to shoot down missiles.• She put the gun back down on the desk.• Submachine guns mowed down students by the hundreds, perhaps by the thousands. 