n 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 syn. T. diversilobum) of the Pacific coast  b  :  a bushy plant (R. toxicodendron syn. T. pubescens) of the southeastern U.S.  2  :  POISON IVY 1a  3  :  a skin rash produced by poison oak .
 
 
 
Similar sounding terms:  pac·ing 
 
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