Omni - all, Uni - one, Sub - under

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Across
  1. 2. having unlimited power; able to do anything.
  2. 4. a mythical animal typically represented as a horse with a single straight horn projecting from its forehead.
  3. 5. an underground electric railroad.
  4. 6. an outlying district of a city, especially a residential one.
  5. 7. a warship with a streamlined hull designed to operate completely submerged in the sea
  6. 9. all existing matter and space considered as a whole; the cosmos.
Down
  1. 1. widely or constantly encountered; common or widespread.
  2. 3. an animal or person that eats food of both plant and animal origin.
  3. 4. the state of being united or joined as a whole.
  4. 8. a cycle with a single wheel