indigo n.

"the Indian subcontinent, central Asia south of the Himalayas," formerly sometimes used generally for "Asia;" since 1947 specifically in reference to the Republic of India, Old English India, Indea, from Latin India, from Greek India "region of the Indus River," later used of the region beyond it, from Indos "Indus River," also "an Indian," from Old Persian Hindu, the name for the province of Sind, from Sanskrit sindhu "river."

The more common Middle English form was Ynde or Inde, from Old French (hence Indies). The form India began to prevail again in English from 16c., perhaps under Spanish or Portuguese influence.

chemical base used in making colorful dyes, 1843, coined 1841 by German chemist Carl Julius Fritzsche and adopted by Hofmann, ultimately from Portuguese anil "the indigo shrub," from Arabic an-nil "the indigo," assimilated from al-nil (with Arabic definite article al-), from Persian nila, ultimately from Sanskrit nili "indigo," from nilah "dark blue."

With suffix -ine indicating "derived substance" (see -ine (1); also see -ine (2) for the later, more precise, use of the suffix in chemistry). Discovered in 1826 in indigo and at first called crystallin; it became commercially important in 1856 when mauve dye was made from it. As an adjective from 1860.