κύανος

Greek kyanos — the blue-green color, the blue stone — appears in Homer's Iliad (8th century BCE) describing the dark blue of a metal helmet: 'with kyanos brows.' The stone kyanos was probably lapis lazuli or a blue frit (an artificial blue glass), prized for its intense color and used in Egyptian blue pigment. Kyanos was the most valuable color in the ancient Mediterranean.

From Greek, kyanos entered Latin as cyanus — the blue cornflower was called cyanus by Pliny the Elder (23-79 CE), because its petals are that particular blue-green. The cornflower (Centaurea cyanus) still carries the etymological color in its species name. Medieval herbalists named plants by their color, and blue plants proliferated under the kyanos lineage.

The color cyan, as we now define it, is the green-blue secondary color in the RGB and CMYK color models — positioned between blue and green. In printing (CMYK: cyan, magenta, yellow, key black), cyan is the blue-ish ink used for a third of all color printing. The ancient Greek word for a blue-green stone is now the name of one of four standard printer inks.

Prussian blue, the first modern synthetic color pigment (accidentally created by Johann Jacob Diesbach in 1704), contains cyanide — the name derived from kyanos because Prussian blue is a cyanide compound. The Greek stone word ended up embedded in one of the most lethal chemical compounds known. The beautiful blue mineral shared its name with the poison.