The Collaborative International Dictionary of English v.0.48:

Swear \Swear\, v. i. [imp. Swore, formerly Sware; p. p.
   Sworn; p. pr. & vb. n. Swearing.] [OE. swerien, AS.
   swerian; akin to D. zweren, OS. swerian, OHG. swerien, G.
   schw["o]ren, Icel. sverja, Sw. sv[aum]rja, Dan. svaerge,
   Icel. & Sw. svara to answer, Dan. svare, Dan. & Sw. svar an
   answer, Goth. swaran to swear, and perhaps to E. swarm.
   [root]177. Cf. Answer.]
   1. To affirm or utter a solemn declaration, with an appeal to
      God for the truth of what is affirmed; to make a promise,
      threat, or resolve on oath; also, to affirm solemnly by
      some sacred object, or one regarded as sacred, as the
      Bible, the Koran, etc.
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            Ye shall swear by my name falsely.    --Lev. xix.
                                                  12.
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            I swear by all the Roman gods.        --Shak.
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   2. (Law) To give evidence on oath; as, to swear to the truth
      of a statement; he swore against the prisoner.
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   3. To make an appeal to God in an irreverant manner; to use
      the name of God or sacred things profanely; to call upon
      God in imprecation; to curse.
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            [I] swore little; diced not above seven times a
            week.                                 --Shak.
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   To swear by, to place great confidence in a person or
      thing; to trust implicitly as an authority. "I simply
      meant to ask if you are one of those who swear by Lord
      Verulam." --Miss Edgeworth.

   To swear off, to make a solemn vow, or a serious
      resolution, to abstain from something; as, to swear off
      smoking. [Slang]
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The Collaborative International Dictionary of English v.0.48:

Swear \Swear\, v. t.
   1. To utter or affirm with a solemn appeal to God for the
      truth of the declaration; to make (a promise, threat, or
      resolve) under oath.
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            Swear unto me here by God, that thou wilt not deal
            falsely with me.                      --Gen. xxi.
                                                  23.
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            He swore consent to your succession.  --Shak.
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   2. (Law) To put to an oath; to cause to take an oath; to
      administer an oath to; -- ofetn followed by in or into;
      as, to swear witnesses; to swear a jury; to swear in an
      officer; he was sworn into office.
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   3. To declare or charge upon oath; as, he swore treason
      against his friend. --Johnson.
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   4. To appeal to by an oath.
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            Now, by Apollo, king,
            Thou swear'st thy gods in vain.       --Shak.
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   To swear the peace against one, to make oath that one is
      under the actual fear of death or bodily harm from the
      person, in which case the person must find sureties that
      he will keep the peace.
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WordNet (r) 3.0 (2006):

swear
    v 1: utter obscenities or profanities; "The drunken men were
         cursing loudly in the street" [syn: curse, cuss,
         blaspheme, swear, imprecate]
    2: to declare or affirm solemnly and formally as true; "Before
       God I swear I am innocent" [syn: affirm, verify,
       assert, avow, aver, swan, swear]
    3: promise solemnly; take an oath
    4: make a deposition; declare under oath [syn: swear,
       depose, depone]
    5: have confidence or faith in; "We can trust in God"; "Rely on
       your friends"; "bank on your good education"; "I swear by my
       grandmother's recipes" [syn: trust, swear, rely,
       bank] [ant: distrust, mistrust, suspect]

Moby Thesaurus II by Grady Ward, 1.0:

85 Moby Thesaurus words for "swear":
   abjure, abuse, acknowledge, adjure, administer an oath, affirm,
   agree, allege, and candle, assert, assert under oath, asseverate,
   assure, attest, aver, avoid, avouch, avow, bear witness,
   believe in, blaspheme, book, certify, confess, count on,
   countersign, covenant, curse, curse and swear, cuss, declare,
   depone, depose, disclose, dysphemize, eschew, execrate, expletive,
   express the belief, forgo, forsake, forswear, give evidence,
   give up, go off, guarantee, have confidence in, imprecate, insist,
   kiss the book, make a promise, oath, pledge, plight, profess,
   promise, put under oath, put upon oath, rely on, renounce,
   scatologize, shun, state, swear by, swear by bell, swear in,
   swear off, swear the truth, swear to, swear to God,
   swear to goodness, talk dirty, testify, throw over, troth,
   trust in, undertake, underwrite, use language, vilify, vouch,
   vouchsafe, vow, warrant, witness