The Collaborative International Dictionary of English v.0.48:

Forswear \For*swear"\, v. t. [imp. Forswore; p. p. Forsworn;
   p. pr. & vb. n. Forswearing.] [OE. forsweren, forswerien,
   AS. forswerian; pref. for- + swerian to swear. See For-,
   and Swear, v. i.]
   1. To reject or renounce upon oath; hence, to renounce
      earnestly, determinedly, or with protestations.
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            I . . . do forswear her.              --Shak.
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   2. To deny upon oath.
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            Like innocence, and as serenely bold
            As truth, how loudly he forswears thy gold!
                                                  --Dryden.
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   To forswear one's self, to swear falsely; to perjure one's
      self. "Thou shalt not forswear thyself." --Matt. v. 33.

   Syn: See Perjure.
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The Collaborative International Dictionary of English v.0.48:

Forswear \For*swear"\, v. i.
   To swear falsely; to commit perjury. --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

forswear
    v 1: formally reject or disavow a formerly held belief, usually
         under pressure; "He retracted his earlier statements about
         his religion"; "She abjured her beliefs" [syn: abjure,
         recant, forswear, retract, resile]