Aerosol: A system of particles suspended in a gas or fog, dispersible in the air.
Agroterrorism: Terrorism involving the alteration or destruction of crops or domesticated farm animals.
Amerithrax: FBI code name for the post–September 11 anthrax attacks.
Antibiotic: Substance produced by one microbe that kills or disables other microbes.
Antibody: A protein found in blood, produced in response to invasion of the body by a microbe or other foreign biological entity, capable of recognizing that entity and promoting its elimination.
Antiserum: Serum (q.v.) containing antibody.
Antiviral (drug): Chemical substance interfering with reproduction or function of a virus.
Antitoxin: Antiserum made against a bacterial toxin.
Aquifer: A geological formation containing water.
Bacillus: Rod-shaped bacterium.
Bacteriophage: A virus that infects bacteria.