The Collaborative International Dictionary of English v.0.48:

Enemy \En"e*my\, n.; pl. Enemies. [OF. enemi, F. ennemi, from
   L. inimicus; in- (negative) + amicus friend. See Amicable.]
   One hostile to another; one who hates, and desires or
   attempts the injury of, another; a foe; an adversary; as, an
   enemy of or to a person; an enemy to truth, or to falsehood.
   [1913 Webster]

         To all good he enemy was still.          --Spenser.
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         I say unto you, Love your enemies.       --Matt. v. 44.
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   The enemy (Mil.), the hostile force. In this sense it is
      construed with the verb and pronoun either in the singular
      or the plural, but more commonly in the singular; as, we
      have met the enemy and he is ours or they are ours.
      [1913 Webster]

            It was difficult in such a country to track the
            enemy. It was impossible to drive him to bay.
                                                  --Macaulay.

   Syn: Foe; antagonist; opponent. See Adversary.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Enemy \En"e*my\, a.
   Hostile; inimical. [Obs.]
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         They . . . every day grow more enemy to God. --Jer.
                                                  Taylor.
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WordNet (r) 3.0 (2006):

enemy
    n 1: an opposing military force; "the enemy attacked at dawn"
    2: an armed adversary (especially a member of an opposing
       military force); "a soldier must be prepared to kill his
       enemies" [syn: enemy, foe, foeman, opposition]
    3: any hostile group of people; "he viewed lawyers as the real
       enemy"
    4: a personal enemy; "they had been political foes for years"
       [syn: foe, enemy] [ant: ally, friend]

Moby Thesaurus II by Grady Ward, 1.0:

105 Moby Thesaurus words for "enemy":
   adversary, adversative, adverse, aggressive, alien, antagonist,
   antagonistic, anti, antipathetic, antithetic, archenemy, assailant,
   attacker, battling, bellicose, belligerent, bitter enemy,
   bloodthirsty, bloody, bloody-minded, chauvinist, chauvinistic,
   clashing, combatant, combative, competitive, competitor, con,
   conflicting, contender, contentious, contestant, contradictory,
   contrary, counter, cross, devil, disaccordant, dissentient,
   emulator, ferocious, fierce, fighting, foe, foeman, fractious,
   full of fight, hawkish, hostile, inimical, invader, jingo,
   jingoish, jingoist, jingoistic, martial, militant, militaristic,
   military, negative, noncooperative, obstinate, offensive,
   open enemy, opponent, opposed, opposing, opposing party, opposite,
   opposite camp, oppositional, oppositive, oppugnant, overthwart,
   perverse, public enemy, pugnacious, quarrelsome, recalcitrant,
   refractory, repugnant, rival, saber-rattling, sanguinary,
   sanguineous, savage, scrappy, soldierlike, soldierly, sworn enemy,
   the loyal opposition, the opposition, the other side,
   trigger-happy, truculent, uncooperative, unfavorable, unfriendly,
   unpacific, unpeaceable, unpeaceful, unpropitious, warlike,
   warmongering, warring



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

ENEMY, international law. By this term is understood the whole body of a
nation at war with another. It also signifies a citizen or subject of such a
nation, as when we say an alien enemy. In a still more extended sense, the
word includes any of the subjects or citizens of a state in amity with the
United States, who, have commenced, or have made preparations for commencing
hostilities against the United States; and also the citizens or subjects of
a state in amity with the United States, who are in the service of a state
at war with them. Salk. 635; Bac. Ab. Treason, G.
     2. An enemy cannot, as a general rule, enter into any contract which
can be enforced in the courts of law; but the rule is not without
exceptions; as, for example, when a state permits expressly its own citizens
to trade with the enemy; and perhaps a contract for necessaries, or for
money to enable the individual to get home, might be enforced. 7 Pet. R.
586.
     3. An alien enemy cannot, in general, sue during the war, a citizen of
the United States, either in the courts of, the United States, or those of
the several states. 1 Kent, Com. 68; 15 John. R. 57 S. C. 16 John. R. 438.
Vide Marsh. Ins. c. 2, s. 1; Park. Ins. Index. h.t.; Wesk. Ins. 197; Phil.
Ins. Index. h.t.; Chit. Comm. Law, Index, h.t.; Chit. Law of Nations,
Index, h.t.
     4. By the term enemy is also understood, a person who is desirous of
doing injury to another. The Latins had two terms to signify these two
classes of persons; the first, or the public enemy, they called hostis, and
the latter, or the private enemy, inimicus.