betrothed to (someone)
Engaged to be married to someone. My sister is betrothed to Lord Alistair, and they will be married in the spring.
betroth (someone or oneself) to (someone)
1. To arrange a marriage between two people. Is it true that Lady Edith's family really betrothed her to that horrid man?
2. To agree or vow to marry someone. A: "Why would Alice betroth herself to someone so disreputable?" B: Well, he does have money."