Medical Definition of poison ivy
1a: a climbing plant of the genus Rhus (R. radicans synonym Toxicodendron radicans) that is especially common in the eastern and central United States, that has leaves in groups of three, greenish flowers, and white berries, and that produces an acutely irritating oil causing a usually intensely itching skin rashb: any of several plants closely related to poison ivy; especially : poison oak 1b
2: a skin rash produced by poison ivy
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