SINCE 1828
upsilon
noun
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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