E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A sort of marriage. A fair was at one time held in Dumfriesshire, at which a young man was allowed to pick out a female companion to live with him. They lived together for twelve months, and if they both liked the arrangement were man and wife. This was called hand-fasting or hand-fastening.
This sort of contract was common among the Romans and Jews, and is not unusual in the East even now.
Knowest thou not that rite, holy man? said A venel .; then I will tell thee. We bordermen . take our wives for a year and a day; that space gone by, each may choose another mate, or, at their pleasure, [they] may call the priest to marry them for life, and this we call handfasting.Sir W. Scott: The Monastery, chap. xxv.