The Collaborative International Dictionary
Crocus of Venus
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.]
(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.
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(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.
Crocus of Venus (Old Chem.), oxide of copper.
Wiktionary
crocus of venus
n. (context chemistry obsolete English) copper oxide