Definition of trefoil
a small European plant of the pea family with yellow flowers and three-lobed cloverlike leaves.
- Genera Trifolium and Lotus, family Leguminosae: several species, in particular the bird’s-foot trefoil
a plant with three-lobed leaves similar to trefoil. an ornamental design of three rounded lobes like a clover leaf, used typically in architectural tracery. a thing having three parts; a set of three:a trefoil of parachutes lowers the shuttle’s used rockets to Earth [as modifier] denoting something shaped in the form of a trefoil leaf:trefoil windows