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

[Middle English, from Anglo-Norman trifoil, from Latin trifolium : tri-, tri- + folium, leaf.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.