1. 主に北米産の種々のブタクサ属の雑草の総称で、花粉は高程度にアレルギーを誘発し多くの花粉症や喘息の原因となる(any of numerous chiefly North American weedy plants constituting the genus Ambrosia that produce highly allergenic pollen responsible for much hay fever and asthma)
2. とげだらけの舌形の葉と黄色の花のある広範囲にわたるヨーロッパの雑草(widespread European weed with spiny tongue-shaped leaves and yellow flowers)