(from Latin trifolium
, three-leaved plant, French trèfle
) is a term in Gothic architecture
given to the ornamental foliation or cusping introduced in the heads of window-lights,
tracery, panellings, etc., in which the center takes the form of a three-lobed leaf
one of the earliest examples being in the plate tracery at Winchester (1222
Trefoil is also a common name for some kinds of clover, who have three-foiled leaves.