assault weapon

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An infantry weapon, such as an assault rifle, designed for individual use.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun US Any select-fire firearm that allows semi-automatic and fully automatic operation, and is used or was once used by a military organization.
• noun US A semi-automatic firearm that resembles a military weapon.