1. 
[syn: gumweed, gum plant, tarweed, rosinweed]
The Collaborative International Dictionary of English v.0.48:
gumweed \gumweed\ n.
   any of various Western American plants of the genus
   Grindelia having resinous leaves and stems formerly used
   medicinally; often poisonous to livestock.
   Syn: gum plant, tarweed, rosinweed, rosin-weed.
        [WordNet 1.5]
WordNet (r) 3.0 (2006):
gumweed
    n 1: any of various western American plants of the genus
         Grindelia having resinous leaves and stems formerly used
         medicinally; often poisonous to livestock [syn: gumweed,
         gum plant, tarweed, rosinweed]