The Collaborative International Dictionary of English v.0.48:

Happen \Hap"pen\ (h[a^]p"p'n), v. i. [imp. & p. p. Happened
   (-p'nd); p. pr. & vb. n. Happening.] [OE. happenen, hapnen.
   See Hap to happen.]
   1. To come by chance; to come without previous expectation;
      to fall out.
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            There shall no evil happen to the just. --Prov. xii.
                                                  21.
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   2. To take place; to occur.
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            All these things which had happened.  --Luke xxiv.
                                                  14.
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   To happen on, to meet with; to fall or light upon. "I have
      happened on some other accounts." --Graunt.

   To happen in, to make a casual call. [Colloq.]
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