WordNet (r) 3.0 (2006):

dog fennel
    n 1: weedy plant of southeastern United States having divided
         leaves and long clusters of greenish flowers [syn: dog
         fennel, Eupatorium capillifolium]
    2: widespread rank-smelling weed having white-rayed flower heads
       with yellow discs [syn: mayweed, dog fennel, stinking
       mayweed, stinking chamomile, Anthemis cotula]