upsilon Hear it!

upsilon definition

up·si·lon (o̵̅o̅p′sə län′, up′-)

noun

  1. the twentieth letter of the Greek alphabet (Y, υ)
  2. ☆ any of a group of short-lived elementary particles having a mass about ten times greater than that of a proton

Etymology: LGr y psilon, lit., simple u (to distinguish from oi, of the same sound in LGr)

Webster's New World College Dictionary Copyright © 2009 by Wiley Publishing, Inc., Cleveland, Ohio.
Used by arrangement with John Wiley & Sons, Inc.

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