1. Intellectually or emotionally overwhelming
   "a mind-boggling display"; "a mind-boggling puzzle"

See also: impressive

• unforethoughtful
• unforfeitable
• unforgettable
• unforgettably
• unforgivable
• unforgivably
• unforgiving
• unforgivingly
• unformatted capacity
• unformed
• unforthcoming
• unfortunate
• unfortunate person
• unfortunately
• unfounded
• unframed
• unfree
• unfreeze
• unfrequented
• unfretted
• unfriended
• unfriendliness
• unfriendly
• unfrightened
• unfrock