Source : Webster's Revised Unabridged Dictionary (1913)

Mayweed \May"weed`\, n. (Bot.)
   (a) 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.
   (b) The feverfew.

Source : WordNet®

mayweed
     n : widespread rank-smelling weed having white-rayed flower
         heads with yellow discs [syn: {dog fennel}, {stinking
         mayweed}, {stinking chamomile}, {Anthemis cotula}]