1. Not known; unfamiliar: a modern-day problem unknown in earlier times.
2. 1. Not identified or ascertained: received flowers from an unknown admirer.
   2. Not established or verified.
3. Not well known or widely known: an unknown artist.

1. 1. A person or thing that is unknown: "the abyss of the unknown" (Helena Petrovna Blavatsky).
   2. A person who is not well known, as to the general public: cast an unknown in the starring role.
2. Mathematics. A quantity of unknown numerical value.

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.