Prefix

1. unsuitable

2. unhelpful

3. impolite

4. indirect

5. inexpensive

6. dislike

7. disagree

8. rewrite

9. miswrite

10. uncountable

11. unhealthy

12. impossible

13. infrequent

14. incorrect

15. triangle

16. ensure

17. misspell

18. bicycle

19. impure

20. bipolar