Uni=one

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Across
  1. 2. a one-wheeled vehicle on which the rider sits and pedals
  2. 3. one of a kind; unusual or rare
  3. 5. moving in only one direction
  4. 6. one sided
  5. 7. one group
Down
  1. 1. to join together into one group
  2. 2. having only one cell
  3. 3. a horse-like fabled animal that has one horn growing out of the middle of its forehead
  4. 4. an instance of saying the same words or sounds at the same time; a group that sounds like one
  5. 6. a one-piece leotard and tights combination