E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A sisterhood instituted in the twelfth century, founded by Lambert Bègue or Lambert le Bègue. The members of the male society were
called Beghards (q.v.). The Béguins were at liberty to quit the cloister, if they chose, and marry. The cap called a beguin was named from this sisterhood.
Secta quædam pestifera illorum qui Beguini vulgariter appellantur, qui se Fratres Pauperes de tertia ordine S. Francisci communiter nominabant, ex quibus plures fuerunt tanquam hæretici condemnati et combusti.Bernard Guido: Life of John, xxii.