1. 
[syn: horseweed, Canadian fleabane, fleabane, Conyza canadensis, Erigeron canadensis]
The Collaborative International Dictionary of English v.0.48:
Horseweed \Horse"weed`\, n. (Bot.)
   A composite plant (Erigeron Canadensis), which is a common
   weed.
   [1913 Webster]
WordNet (r) 3.0 (2006):
Erigeron canadensis
    n 1: common North American weed with linear leaves and small
         discoid heads of yellowish flowers; widely naturalized
         throughout temperate regions; sometimes placed in genus
         Erigeron [syn: horseweed, Canadian fleabane,
         fleabane, Conyza canadensis, Erigeron canadensis]