The Collaborative International Dictionary of English v.0.48:

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.
       [1913 Webster]