1,2 benzopyrone ( C9H6O2 )

(From French coumarine, derived from Spanish cumarú, again derived from a word in a Tupí-Guaraní language)

Coumarin occurs naturally in lavender oil, woodruff, some varieties of grass and in clover. It has a pleasant, vanilla-like odour, which is especially noticeable in dried plants, and which is used in perfume and scented tobacco.

Partially decomposed clover, when used as feed for livestock, causes an illness marked by a severely increased tendency to bleed. The reason is that coumarin is microbiologically converted in the digestive process to dicoumarol, which acts to inhibit the effects of vitamin K on the coagulation of blood. Dicoumarol is used in medicine as an anticoagulant, to treat blood clots in stroke victims.