1. in front at or in the front
  2. inference a conclusion you can draw based on known evidence
  3. indifferent marked by a lack of interest
  4. invariant unvarying in nature
  5. affront a deliberately offensive act
  6. confront oppose, as in hostility or a competition
  7. upfront frank and honest
  8. environment the totality of surrounding conditions
  9. infract act in disregard of laws, rules, contracts, or promises
  10. informant a person who supplies facts, knowledge, or news
  11. infringe advance beyond the usual limit
  12. wavefront (physics) an imaginary surface joining all points in space that are reached at the same instant by a wave propagating through a medium
  13. environs the area in which something exists or lives
  14. infrequent not occurring regularly or at short intervals
  15. inferno a very intense and uncontrolled fire
  16. out front leading or ahead in a competition
  17. invert turn inside out or upside down
  18. irreverent showing lack of due respect or veneration
  19. infarct localized necrosis resulting from obstruction of the blood supply
  20. infirmity the state of being weak in health or body