capsaicin: colorless pungent crystalline compound derived from capsicum; source of the hotness of hot peppers of the genus Capsicum such as chili and cayenne and jalapeno
chemical irritant: a substance producing irritation
gordian knot: an intricate knot tied by Gordius, the king of Phrygia, and cut by the sword of Alexander the Great after he heard that whoever undid it would become ruler of Asia