noun up·si·lon \ˈüp-sə-ˌlän, ˈyüp-, ˈəp-, -lən, British usually yüp-ˈsī-lən\

Definition of upsilon

  1. 1 :  the 20th letter of the Greek alphabet — see alphabet table

  2. 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

Origin and Etymology of upsilon

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

First Known Use: 1621

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clearly seen through or understood

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