a. Emitting light, especially in the dark; shining.
b. Reflecting light; illuminated: "He watched a luminous cloud drifting up from the Gulf" (Tim Gautreaux). See Synonyms at bright.
2. Having a high degree of saturation: a luminous green.
a. Presented or perceived clearly or vividly: luminous memories.
b. Enlightened or intelligent: luminous ideas.
[Middle English, from Old French lumineux, from Latin lūminōsus, from lūmen, lūmin-, light; see leuk- in the Appendix of Indo-European roots.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 by Houghton Mifflin Harcourt Publishing Company. 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:
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.