Blue (blū), n. 1. One of the seven colors into which the rays of light divide themselves, when refracted through a glass prism; the color of the clear sky, or a color resembling that, whether lighter or darker; a pigment having such color. Sometimes, poetically, the sky.
2. A pedantic woman; a bluestocking.
3. pl. [Short for blue devils.] Low spirits; a fit of despondency; melancholy.
Berlin blue, Prussian blue. — Mineral blue. See under Mineral. — Prussian blue. See under Prussian.