1. Threatening or foreshadowing evil or tragic developments
   - baleful, forbidding, menacing, minacious, ominous, sinister, threatening

See also: alarming

• 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