The Collaborative International Dictionary of English v.0.48:

Unfriendly \Un*friend"ly\, a.
   1. Not friendly; not kind or benevolent; hostile; as, an
      unfriendly neighbor.
      [1913 Webster]

   2. Not favorable; not adapted to promote or support any
      object; as, weather unfriendly to health.
      [1913 Webster] -- Un*friend"li*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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

Moby Thesaurus II by Grady Ward, 1.0:

66 Moby Thesaurus words for "unfriendliness":
   aggression, aggressiveness, antagonism, autism, bashfulness,
   bellicism, bellicosity, belligerence, belligerency, chauvinism,
   chill, chilliness, coldness, combativeness, contentiousness,
   coolness, disaffinity, dissociability, enmity, ferocity,
   fierceness, fight, frost, hostility, iciness, incompatibility,
   incompatibleness, inhospitableness, inhospitality, inimicality,
   insociability, jingoism, martialism, militancy, militarism,
   mopishness, moroseness, nonwelcome, personal conflict,
   pugnaciousness, pugnacity, quarrelsomeness, saber rattling,
   self-containment, self-sufficiency, social incompatibility, strain,
   sullenness, tension, truculence, unamiability, uncommunicativeness,
   uncompanionability, uncongeniality, uncordiality, ungeniality,
   ungraciousness, ungregariousness, unhospitableness,
   unneighborliness, unpeacefulness, unreceptiveness, unsociability,
   unsociableness, warmongering, warpath