Medical Definition of poison oak
1: any of several plants included in the genus Rhus or sometimes in the genus Toxicodendron that produce an irritating oil like that of poison ivy:a: a bushy plant (R. diversiloba synonym T. diversilobum) of the Pacific coastb: a bushy plant (R. toxicodendron synonym T. pubescens) of the southeastern United States
2: poison ivy 1a
3: a skin rash produced by poison oak
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