An Etymological Dictionary of Astronomy and Astrophysics

1. A combining form meaning “blue, dark blue,” used in the formation of compound words. Also cyan- before a vowel.
   

2. A combining form representing → cyanide in the formation of chemical compounds.

See also: From Gk. kyanos “dark blue, lapis lazuli,” because of its presence in the Prussian blue, Fe₇(CN)₁₈, a dye which was first accidentally made around 1706, by heating substances containing iron and carbon and nitrogen.