WordWeb Online

1. Not easy to understand or use
   "user-unfriendly"
    
2. Not disposed to friendship or friendliness
   "an unfriendly coldness of manner"; "an unfriendly action to take"
    
3. Not friendly
   "an unfriendly act of aggression"
   - inimical
    
4. Very unfavourable to life or growth
   "the unfriendly environment at high altitudes"
   - hostile, uncongenial

See also: beetle-browed, chilly, cool, friendliness, hostile, incompatible, inhospitable, scowling, uncongenial, uncordial, unfriendliness, unneighborly [US], unneighbourly [Brit, Cdn], unsociable

Antonym: friendly

Encyclopedia: Unfriendly