Quatrefoil

Chambers's Encyclopaedia, Volume 8: Peasant to Eoumelia, p. 523

Quatrefoil, an opening in tracery, a panel, &c., divided by cusps or featherings into four leaves. This form is much used as an ornament in Gothic architecture.

A decorative quatrefoil, which is a four-lobed design with pointed ends, resembling a stylized cross or flower.
Quatrefoil.
Source scan(s): p. 0532