1. Either of two shrubs, Toxicodendron toxicarium (syn. Rhus toxicodendron) of the southeast United States or T. diversilobum (syn. R. diversiloba) of western North America, related to poison ivy and causing a rash on contact.
2. See poison ivy.
3. A skin rash caused by contact with one of these plants.

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.