The Collaborative International Dictionary of English v.0.48:

Defense \De*fense"\, Defence \De*fence"\, n. [F. d['e]fense, OF.
   defense, fem., defens, masc., fr. L. defensa (cf. LL.
   defensum), from defendere. See Defend, and cf. Fence.]
   1. The act of defending, or the state of being defended;
      protection, as from violence or danger.
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            In cases of defense 't is best to weigh
            The enemy more mighty than he seems.  --Shak.
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   2. That which defends or protects; anything employed to
      oppose attack, ward off violence or danger, or maintain
      security; a guard; a protection.
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            War would arise in defense of the right. --Tennyson.
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            God, the widow's champion and defense. --Shak.
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   3. Protecting plea; vindication; justification.
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            Men, brethren, and fathers, hear ye my defense.
                                                  --Acts xxii.
                                                  1.
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   4. (Law) The defendant's answer or plea; an opposing or
      denial of the truth or validity of the plaintiff's or
      prosecutor's case; the method of proceeding adopted by the
      defendant to protect himself against the plaintiff's
      action.
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   5. Act or skill in making defense; defensive plan or policy;
      practice in self defense, as in fencing, boxing, etc.
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            A man of great defense.               --Spenser.
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            By how much defense is better than no skill. --Shak.
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   6. Prohibition; a prohibitory ordinance. [Obs.]
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            Severe defenses . . . against wearing any linen
            under a certain breadth.              --Sir W.
                                                  Temple.
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The Collaborative International Dictionary of English v.0.48:

Defense \De*fense"\, v. t.
   To furnish with defenses; to fortify. [Obs.] [Written also
   defence.]
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         Better manned and more strongly defensed. --Hales.
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WordNet (r) 3.0 (2006):

defense
    n 1: (military) military action or resources protecting a
         country against potential enemies; "they died in the
         defense of Stalingrad"; "they were developed for the
         defense program" [syn: defense, defence, defensive
         measure]
    2: protection from harm; "sanitation is the best defense against
       disease" [syn: defense, defence]
    3: (sports) the team that is trying to prevent the other team
       from scoring; "his teams are always good on defense" [syn:
       defense, defence, defending team] [ant: offence,
       offense]
    4: the justification for some act or belief; "he offered a
       persuasive defense of the theory" [syn: defense, defence,
       vindication]
    5: (psychiatry) an unconscious process that tries to reduce the
       anxiety associated with instinctive desires [syn: defense
       mechanism, defense reaction, defence mechanism, defence
       reaction, defense, defence]
    6: the federal department responsible for safeguarding national
       security of the United States; created in 1947 [syn:
       Department of Defense, Defense Department, United States
       Department of Defense, Defense, DoD]
    7: the defendant and his legal advisors collectively; "the
       defense called for a mistrial" [syn: defense, defence,
       defense team, defense lawyers] [ant: prosecution]
    8: the speech act of answering an attack on your assertions;
       "his refutation of the charges was short and persuasive"; "in
       defense he said the other man started it" [syn: refutation,
       defense, defence]
    9: an organization of defenders that provides resistance against
       attack; "he joined the defense against invasion" [syn:
       defense, defence, defense force, defence force]
    10: a structure used to defend against attack; "the artillery
        battered down the defenses" [syn: defensive structure,
        defense, defence]
    11: a defendant's answer or plea denying the truth of the
        charges against him; "he gave evidence for the defense"
        [syn: defense, defence, denial, demurrer] [ant:
        criminal prosecution, prosecution]
    12: the act of defending someone or something against attack or
        injury; "a good boxer needs a good defense"; "defense
        against hurricanes is an urgent problem" [syn: defense,
        defence]