a. Impenetrable by light; neither transparent nor translucent.
b. Not reflecting light; having no luster: an opaque finish.
2. Impenetrable by a form of radiant energy other than visible light: a chemical solution opaque to x-rays.
a. So obscure as to be unintelligible: "opaque, elusive, minimal meanings" (John Simon).
b. Mentally obtuse; dense.
Something that is opaque, especially an opaque pigment used to darken parts of a photographic print or negative.
[Middle English opake, shady, and French opaque, opaque (from Old French, shady), both from Latin opācus.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 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.