coumarin

noun

cou·​ma·​rin ˈkü-mə-rən 

: a toxic white crystalline lactone C₉H₆O₂ with an odor of new-mown hay found in plants or made synthetically and used especially in perfumery and as a parent compound in anticoagulant agents

also : a derivative of this compound

Examples of coumarin in a Sentence

Recent Examples on the Web

Watch out for coumarin: Cassia cinnamon (Cinnamomum cassia) contains coumarin, a chemical that may harm your liver when consumed in large amounts for prolonged periods or with liver conditions.1 Food-level amounts are generally safe: Cinnamon consumed in amounts used in foods is likely safe. —Jamie Johnson, Verywell Health, 17 Oct. 2025

For example, cinnamon contains powerful antioxidant and anti-inflammatory compounds, including cinnamaldehyde, eugenol, cinnamic acid, and coumarin, that may help lower inflammation and protect cells against oxidative stress. —Jillian Kubala, Health, 14 Oct. 2025

As long as that coumarin molecule is bound to the drug, which is known as Penicillin-PPG (Photocleavable Protecting Groups), the antibiotic remains inactive. —Ben Coxworth, New Atlas, 13 June 2025

Wen: Cassia cinnamon may contain high levels of coumarin, which is a blood thinner. —Katia Hetter, CNN Money, 8 May 2025

Word History

Etymology

French coumarine, from coumarou tonka bean tree, from Spanish or Portuguese; Spanish cumarú, from Portuguese, from Tupi *kumarú, *kumbarú

First Known Use

1830, in the meaning defined above

Medical Definition

coumarin

noun

cou·​ma·​rin ˈkü-mə-rən 

: a toxic white crystalline lactone C₉H₆O₂ with an odor of new-mown hay found in plants or made synthetically and used especially in perfumery and as the parent compound in various anticoagulant agents (as warfarin)

also : a derivative of this compound