Unknown (adjective)

1. Not known or familiar.
2. Not identified or established.
3. Not having been discovered or recognized.

Origin:

Late middle english, from old french unknown, from un- + connu known, from latin cognitus, past participle of cognoscere to know.

Examples:

1. The cause of the disease was unknown.
2. The identity of the attacker remains unknown.
3. The artist remained unknown until his work was discovered by a famous critic.
4. The planet was unknown to astronomers until it was recently discovered.
5. The future is always unknown and uncertain.