The Collaborative International Dictionary of English v.0.48:

Hostile \Hos"tile\, a. [L. hostilis, from hostis enemy: cf. F.
   hostile. See Host an army.]
   Belonging or appropriate to an enemy; showing the disposition
   of an enemy; showing ill will and malevolence, or a desire to
   thwart and injure; occupied by an enemy or enemies; inimical;
   unfriendly; as, a hostile force; hostile intentions; a
   hostile country; hostile to a sudden change.

   Syn: Warlike; inimical; unfriendly; antagonistic; opposed;
        adverse; opposite; contrary; repugnant.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Hostile \Hos"tile\, n.
   An enemy; esp., an American Indian in arms against the
   whites; -- commonly in the plural. [Colloq.] --P. H.
   Sheridan.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Aggressive \Ag*gres"sive\, a. [Cf. F. agressif.]
   1. Tending or disposed to aggress; having or showing
      determination and energetic pursuit of one's own ends at
      the expense of others or mindless of others' needs or
      desires; characterized by aggression; making assaults;
      unjustly attacking; as, an aggressive policy, war, person,
      nation; an aggressive businessman; an aggressive
      basketball player; he was aggressive and imperious in his
      convictions; aggressive drivers. Opposite of
      unaggressive.
      [1913 Webster + WordNet 1.5]

            No aggressive movement was made.      --Macaulay.
      [1913 Webster]

   2. Marked by self-confident ambition, vigorous
      competitiveness, energy and initiative; as, an aggressive
      young executive.

   Syn: enterprising, pushful, pushing, pushy
        [WordNet 1.5]

   3. (Med., Biol.) Tending to grow or spread quickly; as, an
      aggressive tumor. [Narrower terms: invasive (vs.
      noninvasive) ] --AS

   Syn: fast-growing(prenominal)
        [WordNet 1.5]

   4. Tending to initiate unprovoked attacks; initiating
      unprovoked military action; eager to fight; as, aggressive
      acts against another country.

   Syn: belligerent.
        [WordNet 1.5]

   Note: Narrower related terms: {bellicose, combative,
         pugnacious, scrappy, truculent ; {hard-hitting,
         high-pressure ; {hostile (used of attempts to buy or
         take control of a business: "hostile takeover";
         "hostile tender offer"); predatory, rapacious,
         raptorial, ravening, vulturine, vulturous . See also:
         assertive, hostile, offensive.
         [WordNet 1.5] -- {Ag*gres"sive*ly, adv. --
         Ag*gres"sive*ness, n.
         [1913 Webster]

WordNet (r) 3.0 (2006):

hostile
    adj 1: characterized by enmity or ill will; "a hostile nation";
           "a hostile remark"; "hostile actions" [ant: amicable]
    2: not belonging to your own country's forces or those of an
       ally; "hostile naval and air forces" [ant: friendly]
    3: impossible to bring into friendly accord; "hostile factions"
    4: very unfavorable to life or growth; "a hostile climate"; "an
       uncongenial atmosphere"; "an uncongenial soil"; "the
       unfriendly environment at high altitudes" [syn: hostile,
       uncongenial, unfriendly]
    5: unsolicited and resisted by the management of the target
       company ( used of attempts to buy or take control of a
       business); "hostile takeover"; "hostile tender offer";
       "hostile bid"
    n 1: troops belonging to the enemy's military forces; "the
         platoon ran into a pack of hostiles" [ant: friendly]

Moby Thesaurus II by Grady Ward, 1.0:

194 Moby Thesaurus words for "hostile":
   acrid, adversary, adversative, adverse, adversive, against,
   aggressive, alien, allergic, antagonistic, anti, antipathetic,
   antithetic, antonymous, argumentative, at cross-purposes,
   at loggerheads, at odds, at variance, at war, averse, balancing,
   battling, bellicose, belligerent, bitter, bloodthirsty, bloody,
   bloody-minded, breakaway, caustic, chauvinist, chauvinistic,
   clashing, cold, colliding, combative, compensating, competitive,
   con, conflicting, confronting, contentious, contradicting,
   contradictory, contradistinct, contrapositive, contrarious,
   contrary, contrasted, converse, counter, counteractant,
   counteracting, counteractive, counterbalancing, counterpoised,
   countervailing, counterworking, cranky, cross, crotchety,
   dead against, despiteful, detrimental, differing, difficult, dim,
   disaccordant, disaffected, disagreeable, disagreeing, disapproving,
   discordant, discrepant, disenchanted, disharmonious, disinclined,
   displeased, disproportionate, dissentient, dissident, dissonant,
   divergent, dour, enemy, eyeball to eyeball, ferocious, fierce,
   fighting, fractious, full of fight, full of hate, grating, hard,
   harmful, hateful, hawkish, ill, immiscible, in opposition,
   inaccordant, incompatible, inconsistent, inharmonious,
   inhospitable, inimical, inverse, jangling, jarring, jingo,
   jingoish, jingoist, jingoistic, loath, malevolent, malicious,
   malignant, martial, militant, militaristic, military, miserable,
   negative, nonconformist, noncooperative, not charmed, not easy,
   obstinate, obverse, offensive, opponent, opposed, opposing,
   opposite, oppositional, oppositive, oppugnant, out of accord,
   out of whack, overthwart, perverse, pugnacious, put off,
   quarrelsome, rancorous, reactionary, recalcitrant, refractory,
   renitent, repugnant, resistant, reverse, revolutionary, rigorous,
   rival, saber-rattling, sanguinary, sanguineous, savage, scrappy,
   set against, sinister, soldierlike, soldierly, sore, sour,
   spiteful, squared off, stressful, trigger-happy, troublesome,
   troublous, truculent, trying, uncongenial, uncooperative,
   unfavorable, unfriendly, unharmonious, unpacific, unpeaceable,
   unpeaceful, unpropitious, unsympathetic, untoward, variant,
   venomous, virulent, vitriolic, warlike, warmongering, warring,
   wretched