|warfare in which chemicals other than explosives are used as weapons, esp warfare using asphyxiating or nerve gases, poisons, defoliants, etc|
|a children's mummer's parade, as on the Fourth of July, with prizes for the best costumes.|
|an arrangement of five objects, as trees, in a square or rectangle, one at each corner and one in the middle.|
The use of chemical agents as a weapon of war or terror. From the mustard gas used in World War I to the highly lethal neurotoxin Sarin that is potentially available for use today, chemicals are considered a weapon of mass destruction, and their use is condemned by most civilized nations.