1. imperative requiring attention or action
  2. impracticable not capable of being carried out or put into practice
  3. impregnable incapable of being attacked or tampered with
  4. improvable susceptible of improvement
  5. impracticably to an impracticable degree
  6. imperfectible capable of being made imperfect
  7. impermeable preventing especially liquids to pass or diffuse through
  8. imperturbable marked by extreme calm and composure
  9. improvidently in an improvident manner
  10. improbable having a chance of occurring too low to inspire belief
  11. imperviable not admitting of passage or capable of being affected
  12. impregnably in an impregnable manner
  13. impracticability the quality of not being usable
  14. impromptu with little or no preparation or forethought
  15. impressionable easily influenced
  16. unprofitable producing little or no profit or gain
  17. imperceptible impossible or difficult to sense
  18. improvement the act of making something better
  19. impractical not workable
  20. improvidence a lack of prudence, care, or foresight