The Collaborative International Dictionary of English v.0.48:

Crocus \Cro"cus\ (kr[=o]"k[u^]s), n. [L., saffron, fr. Gr.
   kro`kos; cf. Heb. kark[=o]m, Ar. kurkum, Skr. ku[.n]kuma.]
   1. (Bot.) A genus of iridaceous plants, with pretty blossoms
      rising separately from the bulb or corm. Crocus vernus
      is one of the earliest of spring-blooming flowers; Crocus
      sativus produces the saffron, and blossoms in the autumn.
      [1913 Webster]

   2. (Chem.) A deep yellow powder; the oxide of some metal
      calcined to a red or deep yellow color; esp., the oxide of
      iron (Crocus of Mars or colcothar) thus produced from
      salts of iron, and used as a polishing powder.
      [1913 Webster]

   Crocus of Venus (Old Chem.), oxide of copper.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Colcothar \Col"co*thar\ (k[o^]l"k[-o]*th[~e]r), n. [NL.
   colcothar vitrioli, fr. Ar. qolqo[.t]ar.] (Chem.)
   Polishing rouge; a reddish brown oxide of iron, used in
   polishing glass, and also as a pigment; -- called also
   crocus Martis.
   [1913 Webster]