Ammo is a shorthand way to say "ammunition," meaning bullets, gunpowder, and other combat supplies. A war movie might include a scene of soldiers running low on ammo.

Ammo generally refers to a supply of the actual munitions, or exploding substances and projectiles that are put in guns, cannons, and other weapons. A gun without ammo won't actually shoot. This colloquial form of ammunition was first used around 1917, and both are rooted in the Middle French phrase la munition, "fortification" or "defense."

Definitions of ammo
  1. noun
    projectiles to be fired from a gun
    synonyms: ammunition
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    belt, belt ammunition, belted ammunition
    ammunition (usually of small caliber) loaded in flexible linked strips for use in a machine gun
    ammunition consisting of a cylindrical casing containing an explosive charge and a bullet; fired from a rifle or handgun
    canister, canister shot, case shot
    a metallic cylinder packed with shot and used as ammunition in a firearm
    powder and shot
    ammunition consisting of gunpowder and bullets for muskets
    one shot, round, unit of ammunition
    a charge of ammunition for a single shot
    ammunition consisting of a cylindrical metal casing containing an explosive charge and a projectile; fired from a large gun
    tracer, tracer bullet
    ammunition whose flight can be observed by a trail of smoke
    artillery shell
    a shell fired by artillery
    ball cartridge
    a general purpose cartridge having a primer and a ball and a full charge of powder
    blank, blank shell, dummy
    a cartridge containing an explosive charge but no bullet
    cartouch, cartouche
    a cartridge (usually with paper casing)
    shotgun shell
    a shell containing lead shot; used in shotguns
    shell containing lead pellets that explodes in flight
    tank shell
    a shell fired by the cannon on a tank
    whizbang, whizbang shell, whizzbang
    a small high-velocity shell; it makes a whizzing sound followed by a bang when it hits
    type of:
    arms, implements of war, munition, weaponry, weapons system
    weapons considered collectively
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