ageratum
/ˌadʒəˈreɪtəm/noun
Any of various flowering plants constituting the genus Ageratum (family Asteraceae (Compositae)), native chiefly to tropical America; especially any of the many cultivated varieties of A. houstonianum (formerly A. mexicanum) commonly grown in gardens for their clusters of pink, purple, or blue flowers.
Origin
Mid 16th century (in an earlier sense). Originally from classical Latin agēraton, name of a plant, perhaps a species of achillea (Pliny) from Hellenistic Greek ἀγήρατον, name of a plant, perhaps pot marjoram (Dioscorides), use as noun of neuter of ancient Greek ἀγήρατος not growing old from ἀ- + γῆρατ-, γῆρας old age.