1. Not known; unfamiliar: a problem unknown in earlier times.
2. Not identified, ascertained, or established: received flowers from an unknown admirer.
3. Not well known or widely known: an unknown artist.
a. That which is unknown: investigating the unknown.
b. Something that is not known: This case has many unknowns.
c. A person who is not well known, as to the general public: cast an unknown in the starring role.
d. An unknown person, especially an Unknown Soldier: the tomb of the unknowns.
2. Mathematics A quantity of unknown numerical value.
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.