Cassidony \Cas"si*do*ny\, n. [Cf. LL. cassidonium, F. Cassidoine. See {Chalcedony}.] (Bot.) (a) The French lavender ({Lavandula St[oe]chas}). (b) The goldilocks {(Chrysocoma Linosyris)} and perhaps other plants related to the genus {Gnaphalium} or cudweed.