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2.
The thing under the barrel of Tony Montana's M16A2 that shoots grenades.
"SAY HELLO TO MY LITTLE FRIEND!!!"
-Tony Montana as he blows open the door with his M16A2 with M203.
by Tony Scarface Montana September 13, 2008
 
1.
The M203A1 is a 40mm, single shot, breech loaded, pump action, shoulder fired grenade launcher. It is used by both American and Canadian forces. It is mounted under the barrel. It ranges from 100-400m adjustable in 50m increments. The most commonly used rounds are smoke, CS, and HE rounds. It weighs 1.3kg unloaded and 1.8kg loaded depending on the round. It is simple to operate, take apart, and clean.
The M203 Grenadier took out a trench from 350m.
by Brendan September 29, 2004
 
3.
A singular pump action single fire grenade launcher. Fires 40mm high explosive shells. Little kids know this thing as the noob tube.
IRL: "Private! Cover our men using the M203.
C.o.D: "Aww that idiot noobtubed me!"
by Charles Keif February 10, 2014
 
4.
A nubby grenade weapon slung to the underneath of an M4 rifle on the (somewhat)popular online game Soldier Of Fortune 2.

Incredibaly fustrating to be killed by it.
Me: fo m203 nub
Him: lol rofl, owned
by AK God January 01, 2004
 
5.
A grenade launcher usually attached to the bottom of an M-16 or M4 assault rifle. More commonly known to Soldier of Fortune 2 players as the n00b cannon due to the fact it is easy to use and can frag a player in one shot, hence it is a favourite among n00bs.
Shiiiiiit! I just got fragged by that n00b and his M203 n00b cannon.
by Anon. January 11, 2004