adding a suffix to double constant words

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Across
  1. 3. — a person who buys things at a store.
  2. 9. — the most hot; highest in temperature.
  3. 10. — the place or environment where something happens; also adjusting something.
  4. 12. — unfortunate; causing sadness or disappointment.
  5. 14. — happening or taking place.
  6. 16. — moving quickly on foot; also operating or functioning.
Down
  1. 1. — discouraging or preventing someone from doing something.
  2. 2. — covered or enclosed in paper, cloth, or another material.
  3. 4. — pushing or driving something forward.
  4. 5. — seen or noticed; also marked with spots.
  5. 6. — bringing something to an end; causing something not to continue.
  6. 7. — let fall; also decreased or fell suddenly.
  7. 8. — becoming responsible for something, usually a cost or consequence.
  8. 11. — powerful, convincing, or very interesting.
  9. 13. — the start or first part of something.
  10. 15. — turning around rapidly in a circle.