- Not known; unfamiliar: a modern-day problem unknown in earlier times.
- Not identified or ascertained: received flowers from an unknown admirer.
- Not established or verified.
- Not well known or widely known: an unknown artist.
A person or thing that is unknown: “the abyss of the unknown” (Helena Petrovna Blavatsky). A person who is not well known, as to the general public: cast an unknown in the starring role. Mathematics. A quantity of unknown numerical value
In the more advanced planetary ages these seraphim enhance man's appreciation of the truth that uncertainty is the secret of contented continuity. They help the mortal philosophers to realize that, when ignorance is essential to success, it would be a colossal blunder for the creature to know the future. They heighten man's taste for the sweetness of uncertainty, for the romance and charm of the indefinite and unknown future.