poison ivy, any of several species of climbing vine of the genus Rhus, characterized by shiny three-pointed leaves. It is common in North America and causes severe allergic contact dermatitis in many people. Localized vesicular eruption with itching and burning results and may be treated with antipruritic lotions, cool compresses, or topical corticosteroid ointment or cream. Severe cases may require corticosteroids given intramuscularly or orally. See also rhus dermatitis, urushiol.
