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.
      [1913 Webster]

            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:

Sworn \Sworn\,
   p. p. of Swear.
   [1913 Webster]

   Sworn brothers, originally, companions in arms who took an
      oath to share together good and bad fortune; hence,
      faithful friends.

   Sworn enemies, determined or irreconcilable enemies.

   Sworn friends, close friends.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sworn
    adj 1: bound by or as if by an oath; "according to an early
           tradition became his sworn brother"; "sworn enemies"
           [syn: pledged, sworn]
    2: bound by or stated on oath; "now my sworn friend and then
       mine enemy"- Shakespeare [ant: unsworn]

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "sworn":
   affianced, affirmed, alleged, announced, asserted, asseverated,
   assured, attested, averred, avouched, avowed, betrothed, bound,
   certified, committed, compromised, confirmed, contracted, declared,
   deep-dyed, deep-rooted, deep-seated, deposed, dyed-in-the-wool,
   engaged, entrenched, enunciated, guaranteed, intended, manifestoed,
   obligated, pledged, plighted, predicated, professed, promised,
   pronounced, settled, stated, sworn to, underwritten, vouched,
   vouched for, vowed, warranted