The 20th 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 "upsilon" in a sentence
"The first reported discovery of a new particle by Lederman's group turned out to be erroneous; initially dubbed the upsilon, it was famously renamed the "oops-Leon.""
"By changing two letters, we can see how things could have been misinterpreted: an original lambda may look like an upsilon, an original theta may look like an Etruscan ef."
"Scientists recently made sense of an odd jiggle in upsilon andromedae: the wobble's caused by three giant planets orbiting the star."