Cyanide is a compound ion, with a net charge of -1, whose formula is (CN[-]).
Because the cyanide ion binds so strongly to the active metal center of oxygen carrying proteins such as hemoglobin, cyanide can act as a poison deadly to multicellular aerobic creatures using such proteins to support their metabolism.
One must be careful of such poisoning when producing foods and beverages (such as wine) from fruits which have a pit, as these often contain significant quantities of cyanide ion, which can be liberated and concentrated during processing. Bitter almonds from which almond oil and flavoring is made also contain cyanide.
Famous cyanide poisoning incidents: