IPA: /bɪˈtroʊθəl/
KK: /bɪˈtroʊðəl/
A formal agreement between two people to marry each other in the future.
They celebrated their betrothal with a small family gathering.
Betrothal is formed from "be-" (meaning to make or cause) and "troth" (from Old English "treowð", meaning faith or loyalty) and the suffix "-al" (indicating a noun). The word refers to the act of making a promise of faithfulness or loyalty in the context of marriage.
Think of making a promise of 'faith' ('troth') to someone, which is what betrothal means — a commitment to be loyal.