Trefoil :: Trefoil (n.) Any plant of the genus Trifolium, which includes the white clover, red clover, etc.; -- less properly, applied also to the nonesuch, or black medic. See Clover, and Medic..
Trefoil :: Trefoil (n.) An ornamental foliation consisting of three divisions, or foils..
Trefoil :: Trefoil (n.) A charge representing the clover leaf.