• WordNet 3.6
    • adj indigo having a color between blue and violet "indigo flowers"
    • n indigo a blue-violet color
    • n indigo deciduous subshrub of southeastern Asia having pinnate leaves and clusters of red or purple flowers; a source of indigo dye
    • n indigo a blue dye obtained from plants or made synthetically
    • ***

Additional illustrations & photos:

black and white drawing of indigo bird black and white drawing of indigo bird

Webster's Revised Unabridged Dictionary
    • Indigo (Chem) A blue dyestuff obtained from several plants belonging to very different genera and orders, such as, the woad, Isatis tinctoriafamily Cruciferae), Indigofera suffroticosa Indigofera tinctoriafamily Leguminosae), Indigofera Anil Nereum tinctorium Polygonum tinctorium Ait. (family Polygonaceae), etc.; called also natural indigo. It is a dark blue earthy substance, tasteless and odorless, with a copper-violet luster when rubbed. Indigo does not exist in the plants as such, but is obtained by decomposition of the glycoside indican.
    • Indigo A kind of deep blue, one of the seven prismatic colors.
    • a Indigo Having the color of, pertaining to, or derived from, indigo.
    • ***
Century Dictionary and Cyclopedia
    • n indigo A substance obtained in the form of a blue powder from leguminous plants of the genus Indigofera, and used as a blue dye. See indigoplant. Indigo does not exist ready-formed in the indigo-plant, but is produced by the decomposition of a glucoside called indican. The plant is bruised and fermented in vats of water, depositing a blue substance, which is collected and dried in the form of the cubic cakes seen in commerce. In this state indigo has an intensely blue color and an earthy fracture, the kind most esteemed being that which, when rubbed by a hard body, assumes a fine copper-red polish. The indigo of commerce, besides indigo blue, consists of indigo red, indigo brown, and some earthy glutinous matters. Also called Indian blue.
    • n indigo The violet-blue color of the spectrum, extending, according to Helmholtz, from G two thirds of the way to F in the prismatic spectrum. The name was introduced by Newton, but has lately been discarded by the best writers.
    • n indigo An American leguminous plant, Baptisia australis. See Baptisia. Also called blue false indigo and wild indigo.
    • n indigo Same as Japanese indigo.
    • n indigo In Australia, any plant of the genus Swainsona of the bean family, especially S. galegifolia. See Swainsona.
    • ***
Chambers's Twentieth Century Dictionary
    • n Indigo in′di-go a blue dye obtained from the stalks of the indigo plant
    • ***


Webster's Revised Unabridged Dictionary
F. indigo, Sp. indigo, indico, L. indicum, indigo, fr. Indicus, Indian. See Indian
Chambers's Twentieth Century Dictionary
Sp. indico—L. indicum, from Indicus, Indian.


In literature:

You go ahead, and when you're there talk indigo Presbyterian!
"The Long Roll" by Mary Johnston
Next morning, the Kadi paid us a visit, accompanied by a merchant of Damascus, a correspondent of an English house in India for indigo.
"Byeways in Palestine" by James Finn
Persia is a good market for Indian indigo, which has, so far, commanded a ready sale.
"Across Coveted Lands" by Arnold Henry Savage Landor
The very tree trunks stood out as indigo against the sky.
""Wee Tim'rous Beasties"" by Douglas English
Of course, there is an odor about some colored dyes, such as black and indigo blue.
"Five Lectures on Blindness" by Kate M. Foley
He had learned also that indigo is made from the leaves of a plant.
"An American Robinson Crusoe" by Samuel. B. Allison
It is one of the smaller houses erected by Indigo Jones.
"Punch, or the London Charivari, Vol. 146, February 18, 1914" by Various
Blue, in all shades, was the favorite color, and was dyed with indigo.
"Home Life in Colonial Days" by Alice Morse Earle
Indigote: a very deep indigo blue.
"Explanation of Terms Used in Entomology" by John. B. Smith
Here are seen large fields of millet, maize, cotton, and indigo, of the best quality.
"Perils and Captivity" by Charlotte-Adélaïde [née Picard] Dard

In poetry:

Between the indigo mountains fall
White snowflakes:
Robes dyed that hue
Spark such feelings.
"Leg-wearying" by Ise
High over Broadway
A far-flung sign
Glitters in indigo darkness
And spurts again rhythmically,
Spraying great drops
Red as a hemorrhage.
"Flotsam" by Lola Ridge
Red, orange, yellow, green, blue, indigo, violet —
Who is dancing, waving this coloured ribbon against the sky?
The sun returns slanting after the rain
And hill and pass grow a deeper blue.
"Dabodi" by Mao Zedong
Though 'mong the indigo I've wrought
The morning long; through anxious thought
My skirt's filled but in part.
Within five days he was to appear;
The sixth has come and he's not here.
Oh! how this racks my heart!
"A Wife Bemoans Her Husband's Absence" by Confucius
Besides the captain and the mate, the owners and the crew,
The passengers were also drowned excepting only two:
Young PETER GRAY, who tasted teas for BAKER, CROOP, AND CO.,
And SOMERS, who from Eastern shores imported indigo.
"Etiquette" by William Schwenck Gilbert
"But stay," said Mr. PETER: "when in England, as you know,
I earned a living tasting teas for BAKER, CROOP, AND CO.,
I may be superseded - my employers think me dead!"
"Then come with me," said SOMERS, "and taste indigo instead."
"Etiquette" by William Schwenck Gilbert

In news:

Indigo Girls share stage with Alabama Symphony Orchestra in Birmingham.
Sales dip slightly for Indigo Books & Music in Q1.
Web sales declined by 1.1% in Q1 for Indigo Books & Music.
Indigo Kitchen's Lance Knowling enlists in 'Extreme Chef'.
Indigo Girls invite boys to come and play.
Alanis Morissette, the Who, the Indigo Girls, others.
Indigo Girls team with Chattanooga Symphony & Opera.
The Indigo Girls (with the Shadowboxers) keep fans singing along at the Pageant, Saturday, July 21.
Q&A with the Indigo Girl.
For their Paramount Theatre show Friday, the Indigo Girls arrive in a rare configuration: backed by a band, Atlanta's Shadowboxers.
These are the first of my test varieties that I've begun to harvest: ' Indigo Rose' tomato (left) and 'Clara' eggplant (below).
Indigo Rose' is a tasty tomato but ordinary.
Proud Mary shows off new collection at Indigo & Cotton.
Harper Poe, the fashion mastermind behind the local company Proud Mary, is showcasing her brand-new Mali imports at Indigo and Cotton Thurs.
I just LOVE the Indigo Girls.

In science:

The agreement with experiment is clearly good but the Soret (B) band located in the indigo region of the spectrum at 430 nm is slightly redshifted in the calculation, while the red band (Q) has an opposite, blue-shifted behavior.
Turbo charging time-dependent density-functional theory with Lanczos chains
The light-blue, dashed line demonstrates a non-negligible slope of ∼ 25 ± 17 across all of the data, while the indigo, dash-dotted line excludes the two most discrepant points, UV Psc B and YY Gem.
Reevaluating the Mass-Radius Relation for Low-Mass, Main Sequence Stars
If we were to remove those three points (YY Gem appears as a single point), the correlation vanishes and we only observe an offset from the zero point (Indigo dash-dotted line in Figure 4).
Reevaluating the Mass-Radius Relation for Low-Mass, Main Sequence Stars
Each complete run took 22 minutes on an SGI Indigo workstation.
A fast algorithm for random sequential adsorption of discs
Now we expect that more GW detectors will be in operation in the future, in total five detectors including two advanced LIGOs, advanced VIRGO, KAGRA, and IndIGO .
Model-independent test of gravity with a network of ground-based gravitational-wave detectors