biological weapon

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

• noun A biological pathogen or toxin, such as the anthrax bacterium or the smallpox virus, that has been prepared for release on the battlefield or within a civilian population in sufficient concentration to cause widespread illness or death.

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

• noun A biological pathogen or toxin designed or used for warfare.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any weapon usable in biological warfare