pepper spray: a nonlethal aerosol spray made with the pepper derivative oleoresin capiscum; used to cause temporary blindness and incapacitate an attacker; also used as a bear deterrent
chemical weapon: chemical substances that can be delivered using munitions and dispersal devices to cause death or severe harm to people and animals and plants
caesium clock: an atomic clock based on the energy difference between two states of the caesium nucleus in a magnetic field