Trefoil \Tre"foil\, n. [L. tres three + E. foil leaf; cf. F. fr[`e]fle, It. trifoglio, L. trifolium. See Tri-, Foil leaf, and cf. Trifoly.]

1. (Bot.) 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.

2. (Arch.) An ornamental foliation consisting of three divisions, or foils.

3. (Her.) A charge representing the clover leaf.

Source: Webster's Revised Unabridged Dictionary (1913)