名詞 betrothal:

1. a mutual promise to marry
   同義詞：troth, engagement
2. the act of becoming betrothed or engaged
   同義詞：espousal

be.troth.al

n.（名詞）
The act of betrothing or the fact of being betrothed.
訂婚：訂婚的行為或已訂婚的事實(shí)
A mutual promise to marry; an engagement:
婚約：對(duì)結(jié)婚的相互許諾；婚約：
例句：
announced their betrothal the next day.
宣布他們明天訂婚