cyanide
cy·a·nide
noun \ˈsī-ə-ˌnīd, -nəd\Definition of CYANIDE
: any of several compounds (as potassium cyanide) that contain the radical CN having a chemical valence of one, react with and inactivate respiratory enzymes, and are rapidly lethal producing drowsiness, tachycardia, coma, and finally death
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