upsilon
noun
up·si·lon
ˈüp-sə-ˌlän 
ˈyüp-
ˈyüp-
ˈəp-,
-lən,
British usually yüp-ˈsī-lən
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
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The team is hoping to spot composite particles called upsilons, for example.
—
Clara Moskowitz, Scientific American, 14 Feb. 2023
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Clara Moskowitz, Scientific American, 14 Feb. 2023
Cite this Entry
“Upsilon.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/upsilon. Accessed 3 Nov. 2025.
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upsilon
noun
up·si·lon
ˈyüp-sə-ˌlän
ˈəp-
ˈəp-
-lən
: the 20th letter of the Greek alphabet
—Υ or υ
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