| Noun | 1. | Ageratina altissima - American herb having flat-topped clusters of small white flower heads; reputedly a cause of trembles and milk sickness; sometimes placed in genus EupatoriumAgeratina, genus Ageratina - annual to perennial herbs or shrubs of eastern United States and Central and South America herb, herbaceous plant - a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests |