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up·si·lon | \ ˈüp-sə-ˌlän 
, ˈyüp-, ˈəp-, -lən, British usually yüp-ˈsī-lən \
, ˈyüp-, 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
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The first known use of upsilon was in 1621
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