Definitions:

1. an unknown and unexplored region noun
   • they came like angels out the unknown
2. being or having an unknown or unnamed source adjective
   • a poem by an unknown author
3. not known adjective
   • an unknown amount
4. not known to exist adjective
   • things obscurely felt surged up from unknown depths

Synonyms:

• alien
• nameless
• strange
• stranger
• unknown quantity
• unknown region
• unsung