trefoil

Trefoil is a term used to describe objects or designs that have three leaf-like parts. The word comes from Latin tres folia, meaning three leaves. It can refer to botanical, mathematical, architectural, or symbolic forms, all sharing a three-lobed or three-part motif.

In botany, trefoil is a common name for many small legumes with trifoliate leaves, especially in the genus Trifolium. Species such as white clover (Trifolium repens) and red clover (Trifolium pratense) are classic examples. Trefoil leaves typically have three rounded leaflets arranged around a central point, and the plants are valued as forage, ground cover, or ornamental species.

In mathematics, the trefoil knot is the simplest nontrivial knot. It can be represented as a closed loop that crosses itself three times, forming a distinct three-crossing projection. The trefoil knot is chiral, existing in left-handed and right-handed forms, and is a fundamental object of study in knot theory and topology.

Culturally and aesthetically, trefoil shapes occur in heraldry, architecture, and decorative arts. A three-lobed leaf motif is common in heraldic badges and architectural tracery, as well as in logos and emblems. The shamrock, often associated with Ireland, is frequently described as a trefoil, reflecting the symbolic use of the three-leaved form to denote unity, luck, or heritage.

In design, a trefoil arch or window describes a three-lobed arch form created by intersecting circular arcs, producing a characteristic threefold silhouette that appears in various historical styles and ornamental patterns.