Longman Dictionary of Contemporary English
The Collaborative International Dictionary
machine gun \machine gun\ n. A fully automatic rapid-firing rifle, which continues to fire bullets repeatedly as long as the trigger is depressed; lighter versions may be carried in the hands, and heavier versions may be mounted on a tripod, vehicle, or other mount. The lighweight versions are sometimes called a submachine gun.
Wiktionary
n. A type of short range machine gun that is carried as a personal weapon and uses pistol ammunition.
WordNet
n. machine gun that is a portable automatic firearm
Wikipedia
A submachine gun (SMG) is an air-cooled, magazine-fed, automatic carbine designed to fire pistol cartridges. The term "submachine gun" was coined by John T. Thompson, the inventor of the Thompson submachine gun.
The submachine gun was developed during World War I (1914–1918). At its zenith during World War II (1939–1945), millions of SMGs were made. After the war, new SMG designs appeared almost every week. However, by the 1980s, SMG usage decreased. Today, submachine guns have been largely replaced by assault rifles, which have a greater effective range and are capable of penetrating the helmets and body armor used by modern infantrymen. However, submachine guns are still used by military special forces and police SWAT teams for Close Quarters Battle (CQB) because they're "a pistol caliber weapon that's easy to control, and less likely to over-penetrate the target."
There are some inconsistencies in the classification of submachine guns. British Commonwealth sources often refer to SMGs as "machine carbines". Other sources refer to SMGs as "machine pistols" because they fire pistol-caliber ammunition, for example, the MP-40 and MP5, where "MP" stands for Maschinenpistole ("machine pistol" in German). However, the term " machine pistol" is also used to describe a handgun-style firearm capable of fully automatic or burst fire, such as the Stechkin, Beretta 93R and the H&K VP70. Personal Defence Weapons (PDW) such as the FN P90 and H&K MP7 are also commonly referred to as submachine guns. In addition, some compact assault rifles, such as the Colt XM177, HK53 and AKS-74U, are also referred to as SMGs, because they are used in the submachine gun role.
Usage examples of "submachine gun".
As Adele turned, a guard stuck his head and the barrel of his submachine gun around the corner of the bay in which he'd taken refuge.
Ned grabbed the slung submachine gun and aimed toward the doorway.
As Adele turned, a guard stuck his head and the barrel of his submachine gun around the corner of the bay in which hed taken refuge.
Liu Han cradled the submachine gun in her arms as if it were Liu Mei.
In his left hand, gleaming darkly, was a submachine gun, not at the ready, but he started to bring it up—.
In his left hand, gleaming darkly, was a submachine gun, not at the ready, but he started to bring it up-Laura could not blow him away, not without cutting her son down as well-but Chris reacted as Henry Takahami had spent months teaching him to react.
He reached over for the submachine gun, took the clip out that was in the magazine, felt in his pocket for clips, opened the action and looked through the barrel, put the clip back into the groove of the magazine until it clicked, and then looked down the hill slope.
How familiar were these two evil-smelling Brigantes with a Thompson submachine gun?
Deep in one pack he felt the bundled blocks in the sacks, the sacks wrapped in the sleeping robe, and tying the strings of that and pushing the lock shut again, he put his hands into the other and felt the sharp wood outline of the box of the old exploder, the cigar box with the caps, each little cylinder wrapped round and round with its two wires (the lot of them packed as carefully as he had packed his collection of wild bird eggs when he was a boy), the stock of the submachine gun, disconnected from the barrel and wrapped in his leather jacket, the two pans and five clips in one of the inner pockets of the big pack-sack arid the small coils of copper wire and the big coil of light insulated Wire in the other.
The first couple of rounds had been near misses, but then the submachine gun had pulled up and to the right, as such weapons did all too often.
Bracey carried a slung submachine gun, but the ammo tube that should have been parallel to the barrel was missing.