Etymology 16th century (as indico, modern spelling from the 17th century), Spanish índigo, Portuguese endego (modern índigo), or Dutch (via Portuguese) indigo, all from Latin indicum (“indigo”), from Ancient Greek ἰνδικόν (indikón, “Indian dye”), from Ἰνδία (Indía). Doublet of Indic.
1
A purplish-blue color.
2
A greenish dark blue color; the color of indigo dye.
The night was considerably clearer than anybody on board her desired when the schooner Ventura headed for the land. It rose in places, black and sharp against the velvety indigo, over her dipping bow, though most of the low littoral was wrapped in obscurity.1907 January, Harold Bindloss, chapter 6, in The Dust of Conflict, 1st Canadian edition, Toronto, Ont.: McLeod & Allen, →OCLC:
3
A blue-colored dye obtained from certain plants (indigo plant or woad), or a similar synthetic dye.
4
An indigo plant, such as from species in genera Indigofera, Amorpha (false indigo), Baptisia (wild indigo), and Psorothamnus and Dalea (indigo bush).
A Southern planter has been sowing indigo and cotton together. Perhaps he contemplates raising blue cotton; and should he water the plants with nitric acid, he would probably raise gun cotton—if any.1846, editorial staff, “Growing Cotton”, in Scientific American, series 1, Volume 2, Issue 13, page 98:
Etymology 16th century (as indico, modern spelling from the 17th century), Spanish índigo, Portuguese endego (modern índigo), or Dutch (via Portuguese) indigo, all from Latin indicum (“indigo”), from Ancient Greek ἰνδικόν (indikón, “Indian dye”), from Ἰνδία (Indía). Doublet of Indic.