Source : Webster's Revised Unabridged Dictionary (1913)

Unfriendly \Un*friend"ly\, a.
   1. Not friendly; not kind or benevolent; hostile; as, an
      unfriendly neighbor.

   2. Not favorable; not adapted to promote or support any
      object; as, weather unfriendly to health. --
      {Un*friend"li*ness}, n.

Source : WordNet®

unfriendliness
     n 1: dislike experienced as an absence of friendliness [ant: {friendliness}]
     2: an unfriendly disposition [ant: {friendliness}]