The 21st letter of the Greek alphabet. See Table at alphabet.(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.
Use "phi" in a sentence
"The number is termed phi, and like its brother pi, the order of its digits is mysteriously unending and seemingly nonrepeating."
"Yeah, I’m thinking an LPhi-phi is more my speed JWiaDH."
"One of the most ubiquitous metapatterns in nature—a pattern that follows the “Golden Ratio” called phi—is the universal spiral shape that appears in the trails made by subatomic particles, in the double-helix molecule DNA, in seashells, in the movement pattern of the heart, in tornadoes, in galaxies."