mayweed(n = noun.plant) anthemis cotula, dog fennel, stinking chamomile, stinking mayweed - widespread rank-smelling weed having white-rayed flower heads with yellow discs;
is a kind of composite, composite plant
is a member of anthemis, genus anthemis

   A composite plant (Anthemis Cotula), having a strong odor; dog's fennel. It is a native of Europe, now common by the roadsides in the United States. [1913 Webster]

mayweed, n. the stinking camomile, Anthemis cotula.

Etymology:
earlier maidwede f. obs. maithe(n) f. OE magothe, m{aelig}gtha + WEED

corn mayweed, scentless mayweed, stinking mayweed