any of several composite plants of the genus Ageratum, especially A. houstonianum, having heart-shaped leaves and small, dense, blue, lavender, or white flower heads, often grown in gardens.
2.
any of various other composite plants, as the mistflower, having blue or white flowers.
Origin: 1560–70; < Neo-Latin; Latin agēraton < Greek agḗraton, neuter of agḗratos unaging, equivalent to a-a-6 + gērat- (stem of gêras) old age + -os adj. suffix
any tropical American plant of the genus Ageratum, such as A. houstonianum and A. conyzoides, which have thick clusters of purplish-blue flowers
[C16: New Latin, via Latin from Greek agēraton that which does not age, from a-1 + gērat-, stem of gēras old age; the flowers of the plant remain vivid for a long time]