A substance, natural or man-made, which is intrinsically dangerous or otherwise poses a safety hazard. Examples are materials which are explosive, poisonous, chemically active (including acids and other corrosives), radioactive, or biologically active (including human blood and other medical waste).

(law) a breach of contract sufficiently serious to destroy the contract / a breach of a treaty which releases other parties from any obligation under it

(US, law) (in the context of support for terrorism) Any property, or service, including currency or monetary instruments or financial securities, financial services, lodging, training, expert advice or assistance, safe houses, false documentation or identification, communications equipment, facilities, weapons, lethal substances, explosives, personnel, and transportation, except medicine or religious materials

Any material considered crucial to national security concerns and military applications. Examples include natural resources, such as oil; alloys, such as steel, aluminum, and titanium; and composite materials, such as advanced plastics, polymers and ceramics.

Any engineered material composed of two radically different materials in a tightly bonded matrix and having properties significantly different from either constituent

The material used to store genetic information in the nuclei, mitochondria or plastids of an organism's cells; either DNA or RNA

(philosophy, natural science) The stuff or matter of which something is made.

plural of bill of material

(law) A person with information alleged to be material concerning a criminal proceeding, and who therefore may be detained to insure their participation in such a proceeding.

plural of material witness