The Collaborative International Dictionary of English v.0.48:

Combat \Com"bat\ (? or ?; 277), v. i. [imp. & p. p. Combated;
   p. pr. & vb. n. Combating.] [F. combattre; pref. com- +
   battre to beat, fr. L. battuere to strike. See Batter.]
   To struggle or contend, as with an opposing force; to fight.
   [1913 Webster]

         To combat with a blind man I disdain.    --Milton.
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         After the fall of the republic, the Romans combated
         only for the choice of masters.          --Gibbon.
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The Collaborative International Dictionary of English v.0.48:

Combat \Com"bat\, v. t.
   To fight with; to oppose by force, argument, etc.; to contend
   against; to resist.
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         When he the ambitious Norway combated.   --Shak.
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         And combated in silence all these reasons. --Milton.
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         Minds combat minds, repelling and repelled.
                                                  --Goldsmith.

   Syn: To fight against; resist; oppose; withstand; oppugn;
        antagonize; repel; resent.
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The Collaborative International Dictionary of English v.0.48:

Combat \Com"bat\, n. [Cf. F. combat.]
   1. A fight; a contest of violence; a struggle for supremacy.
      [1913 Webster]

            My courage try by combat, if thou dar'st. --Shak.
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            The noble combat that 'twixt joy and sorrow was
            fought in Paulina.                    --Shak.
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   2. (Mil.) An engagement of no great magnitude; or one in
      which the parties engaged are not armies.
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   Single combat, one in which a single combatant meets a
      single opponent, as in the case of David and Goliath;
      also, a duel.

   Syn: A battle; engagement; conflict; contest; contention;
        struggle; fight, strife. See Battle, Contest.
        [1913 Webster]

WordNet (r) 3.0 (2006):

combat
    n 1: an engagement fought between two military forces [syn:
         combat, armed combat]
    2: the act of fighting; any contest or struggle; "a fight broke
       out at the hockey game"; "there was fighting in the streets";
       "the unhappy couple got into a terrible scrap" [syn: fight,
       fighting, combat, scrap]
    v 1: battle or contend against in or as if in a battle; "The
         Kurds are combating Iraqi troops in Northern Iraq"; "We
         must combat the prejudices against other races"; "they
         battled over the budget" [syn: battle, combat]

Moby Thesaurus II by Grady Ward, 1.0:

158 Moby Thesaurus words for "combat":
   Kilkenny cats, action, aerial combat, affray, all-out war,
   altercation, antagonize, appeal to arms, argument, armed combat,
   armed conflict, armored combat, attack, battle, battle royal,
   beat against, beat up against, belligerence, belligerency,
   bickering, bloodshed, box, brawl, breast the wave, broil, brush,
   buck, buffet, buffet the waves, bullfight, cat-and-dog life, clash,
   clash of arms, close, close with, cockfight, collide,
   come to blows, compete with, conflict, confrontation, contend,
   contend against, contention, contentiousness, contest,
   contestation, controversy, cut and thrust, debate, defy,
   difference, disagreement, disputation, dispute, do battle,
   dogfight, duel, embroilment, encounter, engagement, enmity,
   exchange blows, exchange of blows, fence, feud, fight,
   fight a duel, fight against, fighting, fire fight, fray,
   give and take, give satisfaction, grapple, grapple with,
   ground combat, hand-to-hand combat, hand-to-hand fight,
   hostilities, hostility, hot war, house-to-house combat,
   join battle with, jostle, joust, la guerre, labor against,
   litigation, logomachy, might of arms, military operations,
   militate against, mix it up, naval combat, offer resistance,
   open hostilities, open war, oppose, opposition, paper war,
   passage of arms, pitched battle, polemic, quarrel, quarreling,
   quarrelsomeness, rassle, reluct, reluctate, repel, resort to arms,
   riot, rival, rumble, run a tilt, running fight, scramble,
   scrapping, scrimmage, scuffle, shooting war, shoving match,
   skirmish, spar, squabbling, stand-up fight, state of war,
   stem the tide, street fight, strife, strive, strive against,
   struggle, struggle against, take on, tauromachy, the sword,
   thrust and parry, tilt, total war, tourney, traverse, tug-of-war,
   tussle, vendetta, vie with, wage war, war, war of words, warfare,
   warmaking, warring, wartime, withstand, words, wrangling,
   wrestle



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

COMBAT, Eng. law. The form of a forcible encounter between two or more
persons or bodies of men; an engagement or battle. A duel.