The Collaborative International Dictionary of English v.0.48:

Hostility \Hos*til"i*ty\, n.; pl. Hostilities. [L. hostilitas:
   cf. F. hostilit['e].]
   1. State of being hostile; public or private enemy;
      unfriendliness; animosity.
      [1913 Webster]

            Hostility being thus suspended with France.
                                                  --Hayward.
      [1913 Webster]

   2. An act of an open enemy; a hostile deed; especially in the
      plural, acts of warfare; attacks of an enemy. See
      hostilities
      [1913 Webster]

            He who proceeds to wanton hostility, often provokes
            an enemy where he might have a friend. --Crabb.

   Syn: Animosity; enmity; opposition; violence; aggression;
        contention; warfare.
        [1913 Webster]

WordNet (r) 3.0 (2006):

hostility
    n 1: a hostile (very unfriendly) disposition; "he could not
         conceal his hostility" [syn: hostility, ill will]
    2: a state of deep-seated ill-will [syn: hostility, enmity,
       antagonism]
    3: the feeling of a hostile person; "he could no longer contain
       his hostility" [syn: hostility, enmity, ill will]
    4: violent action that is hostile and usually unprovoked [syn:
       aggression, hostility]

Moby Thesaurus II by Grady Ward, 1.0:

142 Moby Thesaurus words for "hostility":
   Kilkenny cats, abhorrence, abomination, action, aggression,
   aggressiveness, allergy, altercation, animosity, animus,
   antagonism, anteposition, antipathy, antithesis, argument,
   aversion, bad blood, bad feeling, bellicism, bellicosity,
   belligerence, belligerency, bickering, bloodshed, cat-and-dog life,
   chauvinism, clash, clashing, cold sweat, collision, combat,
   combativeness, competition, conflict, confrontation, confrontment,
   contention, contentiousness, contest, contestation, contradiction,
   contradistinction, contraindication, contraposition, contrariety,
   contrariness, contrast, controversy, counterposition,
   creeping flesh, cross-purposes, cut and thrust, debate,
   despitefulness, disaccord, disaffinity, disagreement, discrepancy,
   disgust, disputation, dispute, dissension, enmity, ferocity,
   fierceness, fight, fighting, fractiousness, friction,
   hard feelings, hardheartedness, hate, hatred, horror, hostilities,
   ill will, immediate dislike, inconsistency, inimicalness, jingoism,
   litigation, loathing, logomachy, malevolence, malice, malignity,
   martialism, militancy, militarism, mortal horror, nausea,
   negativeness, noncooperation, obstinacy, opposing, oppositeness,
   opposition, opposure, oppugnance, oppugnancy, paper war,
   personality conflict, perverseness, perversity, polar opposition,
   polarity, polarization, polemic, posing against, pugnaciousness,
   pugnacity, quarrel, quarreling, quarrelsomeness, rancor,
   recalcitrance, refractoriness, repugnance, repulsion, rivalry,
   saber rattling, scrapping, showdown, shuddering, spite,
   spitefulness, squabbling, state of war, strife, struggle,
   truculence, uncooperativeness, unfriendliness, unpeacefulness,
   vying, war, war of words, warfare, warmongering, warpath, words,
   wrangling



Bouvier's Law Dictionary, Revised 6th Ed (1856):

HOSTILITY. A state of open enmity; open war. Wolff, Dr. de la Rat. Sec.
1191. Hostility, as it regards individuals, may be permanent or temporary;
it is permanent when the individual is a citizen or subject of the
government at war, and temporary when he happens to be domiciliated or
resident in the country of one of the belligerents; in this latter case the
individual may throw off the national character he has thus acquired by
residence, when he puts himself in motion, bona fide, to quit the country
sine animo revertendi. 3 Rob. Adm. Rep. 12; 3 Wheat. R. 14.
     2. There may be a hostile character merely as to commercial purposes,
and hostility may attach only to the person as a temporary enemy, or it may
attach only to the property of a particular description. This hostile
character in a commercial view, or one limited to certain intents and
purposes only, will attach in, consequence of having possessions in the
territory of the enemy, or by maintaining a commercial establishment there,
or by a personal residence, or, by particular modes of traffic, as by
sailing under the enemy's flag of passport. 9 Cranch, 191 5 Rob. Adm. Rep.
21, 161; 1 Kent Com. 73; Wesk. on Ins. h.t.; Chit. Law of Nat. Index, h.t.



The Devil's Dictionary (1881-1906):

HOSTILITY, n.  A peculiarly sharp and specially applied sense of the
earth's overpopulation.  Hostility is classified as active and
passive; as (respectively) the feeling of a woman for her female
friends, and that which she entertains for all the rest of her sex.