In'di-go, n.

n. [Sp. & Fr. indigo, It. indaco, O. Sp. endico, Pr. indi, endi, O. Fr. inde, from Lat. indicum, indigo, from Indicus, Indian, from India, India.] A blue coloring matter obtained from the Indigofera tinctoria, woad, and other plants, and formed by the decomposition of a peculiar substance called indican, which is supposed to exist in the juices of the plants.

Indigo is obtained by steeping the plant in water till the indican is decomposed by fermentation, when the indigo is precipitated in the form of a blue sediment, which forms the indigo of commerce. It is a uniform dark-blue color, slightly conchoidal fracture, assuming a coppery luster by friction with a hard body, is lighter than water, and insoluble in water, and nearly so in ether or alcohol. Eng. Cyc.