General stuff

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Across
  1. 3. Synonym for barrier
  2. 4. One small step for man, is one giant leap for _______
  3. 6. Highest mountain above sea level
  4. 9. The most oldest institution of learning in the USA
  5. 10. The study of life and living organisms
  6. 12. A plant fiber
  7. 13. It's a ____!
  8. 14. Where porcelain was invented
  9. 15. Honesty is the best policy (e.g)
  10. 16. It's clearly recycable!
  11. 18. A word that sounds like someone you would hang out with
Down
  1. 1. Second president of the USA
  2. 2. When multiple words have the same meaning
  3. 5. Common symptom of flu
  4. 7. Writing text again to improve clarity
  5. 8. What this is
  6. 11. Cats always land on their feet (e.g)
  7. 12. Admit
  8. 13. Happens every four years
  9. 17. One of the only words to have four Z's