1. Not based on reason
   "there is a great deal that is nonrational in modern culture" 
2. Obtained through intuition rather than from reasoning or observation
   - intuitive, visceral

See also: illogical, irrational, unlogical

• unimpaired
• unimpassioned
• unimpeachable
• unimpeachably
• unimpeded
• unimportance
• unimportant
• unimposing
• unimpregnated
• unimpressed
• unimpressionable
• unimpressive
• unimpressively
• unimprisoned
• unimproved
• unincorporated
• unindustrialised
• unindustrialized
• uninebriated
• uninfected
• uninflected
• uninfluenced
• uninfluential
• uninformative
• uninformatively