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.
There shall no evil happen to the just. --Prov. xii.
2. To take place; to occur.
All these things which had happened. --Luke xxiv.
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.]