any of numerous chiefly North American weedy plants constituting the genus Ambrosia that produce highly allergenic pollen responsible for much hay fever and asthma पर्याय: ambrosia, bitterweed,
widespread European weed having yellow daisylike flowers; sometimes an obnoxious weed and toxic to cattle if consumed in quantity पर्याय: ragwort, tansy ragwort, benweed, Senecio jacobaea,