Source : Webster's Revised Unabridged Dictionary (1913)

Handfast \Hand"fast`\, v. t. [imp. & p. p. {Handfasted}; p. pr.
   & vb. n. {Handfasting}.]
   To pledge; to bind; to betroth by joining hands, in order to
   cohabitation, before the celebration of marriage. [Obs.]