The Collaborative International Dictionary of English v.0.48:

Martial \Mar"tial\, a. [F., fr. L. martialis of or belonging to
   Mars, the god of war. Cf. March the month.]
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   1. Of, pertaining to, or suited for, war; military; as,
      martial music; a martial appearance. "Martial equipage."
      --Milton.
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   2. Practiced in, or inclined to, war; warlike; brave.
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            But peaceful kings, o'er martial people set,
            Each other's poise and counterbalance are. --Dryden.
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   3. Belonging to war, or to an army and navy; -- opposed to
      civil; as, martial law; a court-martial.
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   4. Pertaining to, or resembling, the god, or the planet,
      Mars. --Sir T. Browne.
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   5. (Old Chem. & Old Med.) Pertaining to, or containing, iron;
      chalybeate; as, martial preparations. [Archaic]
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   Martial flowers (Med.), a reddish crystalline salt of iron;
      the ammonio-chloride of iron. [Obs.]

   Martial law, the law administered by the military power of
      a government when it has superseded the civil authority in
      time of war, or when the civil authorities are unable to
      enforce the laws. It is distinguished from military law,
      the latter being the code of rules for the regulation of
      the army and navy alone, either in peace or in war.
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   Syn: Martial, Warlike.

   Usage: Martial refers more to war in action, its array, its
          attendants, etc.; as, martial music, a martial
          appearance, a martial array, courts-martial, etc.
          Warlike describes the feeling or temper which leads to
          war, and the adjuncts of war; as, a warlike nation,
          warlike indication, etc. The two words are often used
          without discrimination.
          [1913 Webster]

WordNet (r) 3.0 (2006):

martial
    adj 1: (of persons) befitting a warrior; "a military bearing"
           [syn: soldierly, soldierlike, warriorlike,
           martial]
    2: suggesting war or military life [syn: warlike, martial]
    3: of or relating to the armed forces; "martial law"
    n 1: Roman poet noted for epigrams (first century BC)

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "martial":
   aggressive, antagonistic, battling, bellicose, belligerent,
   bloodthirsty, bloody, bloody-minded, brave, chauvinist,
   chauvinistic, combative, contentious, courageous, enemy, ferocious,
   fierce, fighting, full of fight, hawkish, high-spirited, hostile,
   inimical, jingo, jingoish, jingoist, jingoistic, mettlesome,
   militant, militaristic, military, offensive, pugnacious,
   quarrelsome, saber-rattling, sanguinary, sanguineous, savage,
   scrappy, soldierlike, soldierly, spirited, stalwart, staunch,
   trigger-happy, truculent, unfriendly, unpacific, unpeaceable,
   unpeaceful, valiant, valorous, warlike, warmongering, warring