HERE IS THE SINGULAR. WHAT IS THE PLURAL? SOME ARE THE SAME.

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Across
  1. 1. cherub
  2. 5. radius
  3. 9. analysis
  4. 10. offspring
  5. 11. series
Down
  1. 2. headquarters
  2. 3. index
  3. 4. diagnosis
  4. 6. focus
  5. 7. fungus
  6. 8. alumnus