A type of English finger ring received by a widow who took a vow of chastity that prevented her from making a second marriage which would confer on her second husband the property she had received from her first husband; but in rare instances the vow could be set aside, e.g. by Eleanor, sister of Henry III, whose first husband was William, Earl of Pembroke, and who later married Simon de Montfort, Earl of Leicester (1208-65).
From: An Illustrated Dictionary of Jewelry, autor: Harold Newman, publishers: Thames and Hudson