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
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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
Cite this Entry
“Coumarin.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/coumarin. Accessed 1 Nov. 2025.
Copy CitationMedical 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
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