The Collaborative International Dictionary of English v.0.48:

Desponsage \De*spon"sage\, n. [From L. desponsus, p. p. See
   Despond.]
   Betrothal. [Obs.]
   [1913 Webster]

         Ethelbert . . . went peaceably to King Offa for
         desponsage of Athilrid, his daughter.    --Foxe.
   [1913 Webster]