n 1 a  :  a climbing plant of the genus Rhus (R. radicans syn. Toxicodendron radicans) that is esp. common in the eastern and central U.S., that has leaves in groups of three, greenish flowers, and white berries, and that produces an acutely irritating oil causing a usu. intensely itching skin rash  b  :  any of several plants closely related to poison ivy : esp  :  POISON OAK 1b  2  :  a skin rash produced by poison ivy .
 
 
 
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