\In"di*go\, n.; pl. {Indigoes}. [F. indigo, Sp. indigo,
indico, L. indicum indigo, fr. Indicus Indian. See {Indian}.]
1. A kind of deep blue, one of the seven prismatic colors.
2. (Chem.) A blue dyestuff obtained from several plants
   belonging to very different genera and orders; as, the
   woad, {Isatis tinctoria}, {Indigofera tinctoria}, {I.
   Anil}, {Nereum tinctorium}, etc. 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.
Note: Commercial indigo contains the essential coloring
      principle indigo blue or indigotine, with several other
      dyes; as, indigo red, indigo brown, etc., and various
      impurities. Indigo is insoluble in ordinary reagents,
      with the exception of strong sulphuric acid.
{Chinese indigo} (Bot.), {Isatis indigotica}, a kind of woad.
{Wild indigo} (Bot.), the American herb {Baptisia tinctoria}
   which yields a poor quality of indigo, as do several other
   species of the same genus.

\In"di*go\, a.
Having the color of, pertaining to, or derived from, indigo.
{Indigo berry} (Bot.), the fruit of the West Indian shrub
   {Randia aculeata}, used as a blue dye.
{Indigo bird} (Zo["o]l.), a small North American finch
   ({Cyanospiza cyanea}). The male is indigo blue in color.
   Called also {indigo bunting}.
{Indigo blue}.
(a) The essential coloring material of commercial indigo,
    from which it is obtained as a dark blue earthy powder,
    with a reddish luster, {C16H10N2O2}, which may be
    crystallized by sublimation. Indigo blue is also made
    from artificial amido cinnamic acid, and from artificial
    isatine; and these methods are of great commercial
    importance. Called also {indigotin}.
(b) A dark, dull blue color like the indigo of commerce.
{Indigo brown} (Chem.), a brown resinous substance found in
   crude indigo.
{Indigo copper} (Min.), covellite.
{Indigo green}, a green obtained from indigo.
{Indigo plant} (Bot.), a leguminous plant of several species
   (genus {Indigofera}), from which indigo is prepared. The
   different varieties are natives of Asia, Africa, and
   America. Several species are cultivated, of which the most
   important are the {I. tinctoria}, or common indigo plant,
   the {I. Anil}, a larger species, and the {I. disperma}.
{Indigo purple}, a purple obtained from indigo.
{Indigo red}, a dyestuff, isomeric with indigo blue, obtained
   from crude indigo as a dark brown amorphous powder.
{Indigo snake} (Zo["o]l.), the gopher snake.
{Indigo white}, a white crystalline powder obtained by
   reduction from indigo blue, and by oxidation easily
   changed back to it; -- called also {indigogen}.
{Indigo yellow}, a substance obtained from indigo.