Definition of "trefoil" [tre•foil]

• Any of various plants of the genera Trifolium, Lotus, and related genera of the pea family, having compound trifoliate leaves. (noun)
• An ornament, symbol, or architectural form having the appearance of a trifoliate leaf. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "It is sometimes designated by the term trefoil, three leaved."
• "* Hmmm. Sweet trefoil is purportedly yet another name for this close fenugreek relation."
• "Friedman combined these by twisting wire to form the simplest knot there is - an overhand knot mathematicians call a trefoil - and then dipping it into soapy water."