Suffixes!

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Across
  1. 3. add -ness to happy
  2. 5. add -ness to creepy
  3. 7. add -ness to soft
  4. 10. add -ous to danger
  5. 11. add -ous to homour
Down
  1. 1. add -ness to kind
  2. 2. add -ness to sleepy
  3. 4. add -ness to sick
  4. 6. add -ous to poison
  5. 8. add -ous to envy
  6. 9. add -ous to joy