up·​si·​lon | \ ˈüp-sə-ˌlän How to pronounce upsilon (audio) , ˈyüp- How to pronounce upsilon (audio) , ˈəp-, -lən, British usually yüp-ˈsī-lən \

Definition of upsilon

1 : the 20th letter of the Greek alphabet — see Alphabet Table
2 : any of a group of unstable electrically neutral elementary particles of the meson family that have a mass about 10 times that of a proton

First Known Use of upsilon

1621, in the meaning defined at sense 1

History and Etymology for upsilon

Middle Greek y psilon, literally, simple y; from the desire to distinguish it from oi, which was pronounced the same in later Greek

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The first known use of upsilon was in 1621

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Last Updated

27 Jan 2020

Cite this Entry

“Upsilon.” The Dictionary, Merriam-Webster Inc., Accessed 29 January 2020.

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Rhyming Dictionary: Words that rhyme with upsilon

Comments on upsilon

What made you want to look up upsilon? Please tell us where you read or heard it (including the quote, if possible).


to assert without proof or before proving

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