WordNet (r) 3.0 (2006):

scentless hayweed
    n 1: ubiquitous European annual weed with white flowers and
         finely divided leaves naturalized and sometimes cultivated
         in eastern North America; sometimes included in genus
         Matricaria [syn: scentless camomile, scentless false
         camomile, scentless mayweed, scentless hayweed, corn
         mayweed, Tripleurospermum inodorum, Matricaria
         inodorum]