Prefixes 6,7,8

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Across
  1. 4. eight notes in a musical scale
  2. 8. it's a scary time of year
  3. 9. eight babies, born at once
  4. 10. a sea creature with eight tentacles
  5. 11. a group of seven musicians
  6. 13. an adjective for octagon
  7. 15. an eight-letter word, two months before the new year
  8. 16. an eight-sided shape
  9. 17. someone who is ten years younger than a centenarian
Down
  1. 1. a seven-sided shape
  2. 2. a shape with nine sides
  3. 3. seven babies, all born at once, from the same mother
  4. 5. another word for a seventy-year old
  5. 6. a ten letter word to do with sports
  6. 7. a 3-D shape, two square-based pyramids on top of each other
  7. 8. another word for a eighty-year old
  8. 12. a group of eight musicians
  9. 14. the month of Ms. McLaughlin's birthday