The Collaborative International Dictionary of English v.0.48:

Inimical \In*im"i*cal\ (?; 277), a. [L. inimicalis, fr. inimicus
   unfriendly, hostile; pref. in- not + amicus friendly. See
   Amity.]
   [1913 Webster]
   1. Having the disposition or temper of an enemy; unfriendly;
      unfavorable; -- chiefly applied to private, as hostile is
      to public, enmity.
      [1913 Webster]

   2. Opposed in tendency, influence, or effects; antagonistic;
      inconsistent; incompatible; adverse; repugnant.
      [1913 Webster]

            We are at war with a system, which, by its essence,
            is inimical to all other governments. --Burke.
      [1913 Webster]

WordNet (r) 3.0 (2006):

inimical
    adj 1: not friendly; "an unfriendly act of aggression"; "an
           inimical critic" [syn: unfriendly, inimical]