sesquiterpene lactone
[ˌseskwiˈtə:pi:n ˈlæktəun]
Sesquiterpene lactones are a class of chemical compounds; they are sesquiterpenoids (built from three isoprene units) and contain a lactone ring, hence the name. They are found in many plants and can cause allergic reactions and toxicity if overdosed, particularly in grazing livestock.