be·troth 
(bĭ-trōth, -trôth)
(bĭ-trōth, -trôth)tr.v. be·trothed, be·troth·ing, be·troths
To promise to give in marriage: was betrothed to a member of the royal family.
[Middle English bitrouthen : bi-, be- + trouth, troth (from Old English trēowth; see deru- in the Appendix of Indo-European roots).]