Handfasting is an old word doing new work. In sixteenth century Britain to handfast was to strike a bargain by clasping hands, and the term was used both for betrothal and, in some Scottish parish records, for an informal marriage entered into before a priest could be reached, a practical stopgap in a scattered rural population rather than a sanctioned alternative rite. That older custom died out with better roads and closer churches, and the phrase lay unused for three centuries.
Gerald Gardner and the early Wiccan covens of the mid twentieth century revived the word for a different purpose: a wedding rite for a religion with no existing marriage service to borrow, built from ceremonial magic's cast circle and the seasonal calendar the new movement was already keeping. The cord binding the joined hands, the central visual image now associated with the word, appears to be a twentieth century addition rather than a survival, chosen because it made concrete what handfasting means, a tie made by choice and witnessed by a community, at the moment vows are exchanged. From that small revival the rite has spread well beyond Wicca into the wider modern Pagan movement, and beyond Paganism again into secular and interfaith weddings drawn to its imagery, so that a word once specific to Scottish custom law now names a family of ceremonies performed under a great many skies.