Boyd’s Bible Dictionary:

(in promise). To pledge troth, that is, engage to marry. A betrothed woman was regarded as the lawful wife of her spouse, and he could not break off the match without a divorce, while she, if unfaithful, would be considered an adulteress.

Concise Bible Dictionary:

Among the Jews this was looked upon as being as binding as marriage, and could not be dissolved except by divorce. Certain laws were given as to a betrothed woman (Ex. 21:8-98If she please not her master, who hath betrothed her to himself, then shall he let her be redeemed: to sell her unto a strange nation he shall have no power, seeing he hath dealt deceitfully with her. 9And if he have betrothed her unto his son, he shall deal with her after the manner of daughters. (Exodus 21:8‑9); Deut. 20:77And what man is there that hath betrothed a wife, and hath not taken her? let him go and return unto his house, lest he die in the battle, and another man take her. (Deuteronomy 20:7); Deut. 28:3030Thou shalt betroth a wife, and another man shall lie with her: thou shalt build an house, and thou shalt not dwell therein: thou shalt plant a vineyard, and shalt not gather the grapes thereof. (Deuteronomy 28:30)). Mary, the mother of the Lord Jesus, was betrothed to Joseph, and he contemplated putting her away privately, but was instructed as to the truth of her condition by the angel of the Lord (Matt. 1:18-1918Now the birth of Jesus Christ was on this wise: When as his mother Mary was espoused to Joseph, before they came together, she was found with child of the Holy Ghost. 19Then Joseph her husband, being a just man, and not willing to make her a publick example, was minded to put her away privily. (Matthew 1:18‑19); Luke 1:2727To a virgin espoused to a man whose name was Joseph, of the house of David; and the virgin's name was Mary. (Luke 1:27); Luke 2:55To be taxed with Mary his espoused wife, being great with child. (Luke 2:5)). It is used symbolically to express Jehovah’s favor to His ancient people in a future day, when He will “betroth” them to Himself forever (Hos. 2:19-2019And I will betroth thee unto me for ever; yea, I will betroth thee unto me in righteousness, and in judgment, and in lovingkindness, and in mercies. 20I will even betroth thee unto me in faithfulness: and thou shalt know the Lord. (Hosea 2:19‑20)). Also as to the position in which the church stands to Christ: Paul wrote to the Corinthian saints “I have espoused you to one husband, that I may present you as a chaste virgin to Christ” (2 Cor. 2:22For if I make you sorry, who is he then that maketh me glad, but the same which is made sorry by me? (2 Corinthians 2:2)). The conduct of the saints should be true to this betrothal.

From Manners and Customs of the Bible:

The former part of this passage has reference, doubtless, to the betrothal; the latter part, to the marriage. About a year usually elapsed between betrothal and marriage, though this was not always the case. The expression “after a time,” literally, after days, is sometimes equivalent to a year.