E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A snaky complication on the rod or caduceus of Mercury, adopted by the Grecian brides as the fastening of their woollen girdles, which only the bridegroom was allowed to untie when the bride retired for the night. As he did so he invoked Juno to render his marriage as fecund as that of Hercules, whose numerous wives all had families, amongst them being the fifty daughters of Thestius, each of whom conceived in one night. (See KNOT.)