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in·di·go (ĭndĭ-gō)
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n. pl. in·di·gos or in·di·goes
1.
a. Any of various shrubs or herbs of the genus Indigofera in the pea family, having pinnately compound leaves and usually red or purple flowers in axillary racemes.
b. A dark blue crystalline compound, C16H10N2O2, that is obtained from these plants or produced synthetically and is widely used as a textile dye. Also called indigotin.
2. Any of several related plants, especially those of the genera Amorpha and Baptisia.
3. The hue of that portion of the visible spectrum lying between blue and violet, evoked in the human observer by radiant energy with wavelengths of approximately 420 to 450 nanometers; a dark blue to grayish purple blue.

[Spanish índigo and Dutch indigo (from Portuguese endego), both from Latin indicum, from Greek Indikon (pharmakon), Indian (dye), neuter of Indikos, of India, from India, India, from Indos, the Indus River, from Old Persian Hinduš, Sind; see HINDI.]

indi·go adj.

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. All rights reserved.
 

Indo-European & Semitic Roots Appendices

    Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:

    Indo-European Roots

    Semitic Roots

    The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.