The Collaborative International Dictionary of English v.0.48:

Sponsal \Spon"sal\ (sp[o^]n"sal), a. [L. sponsalis, fr. sponsus
   a betrothal, fr. spondere, sponsum, to betroth. See Spouse,
   and cf. Espousal, Spousal.]
   Relating to marriage, or to a spouse; spousal.
   [1913 Webster]