Source : Webster's Revised Unabridged Dictionary (1913)

Betrothal \Be*troth"al\, n.
   The act of betrothing, or the fact of being betrothed; a
   mutual promise, engagement, or contract for a future marriage
   between the persons betrothed; betrothment; affiance. ``The
   feast of betrothal.'' --Longfellow.

Source : WordNet®

betrothal
     n 1: a mutual promise to marry [syn: {troth}, {engagement}]
     2: the act of becoming betrothed or engaged [syn: {espousal}]