The Probert Encyclopaedia of Heraldry

LOZENGE

In heraldry, a lozenge is a diamond-shaped figure usually with the upper and lower angles slightly acute, borne upon a shield or escutcheon. The term also describes a form of the escutcheon used by women (with the exception in English heraldry of the Sovereign) instead of the shield which is used by men. The use of the lozenge in place of the shield for bearing the arms of a lady was introduced into English heraldry in the beginning of the 14th century.
Research Lozenge