upsilon; Υ, υ +

(Greek: the twentieth letter of the Greek alphabet; Υ, υ; upsilon symbol with hook, ϒ)

upsiloid, ypsiloid, hypsiloid, ypsiliform
Shaped like the Greek letter upsilon (Υ, υ), and English U or V.
upsilon particle
1. In particle physics, a heavy, short-lived particle consisting of a bottom quark bound to its anti-quark; thus, the fifth-quark analog to the J particle.

Eleven additional particles with this quark structure have been identified so far.

2. One of a family of elementary particles having about ten times the mass of the proton and consisting of an atom-like combination of a bottom quark with its anti-quark.
upsilon, ypsilon (smooth y)
1. The 20th letter and sixth vowel of the Greek alphabet (Υ, υ), represented in the English alphabet as "y" or "u"; having the sound of French u, Latin and Old English y.
2. In physics, any of several ephemeral particles whose mass is ten times that of a proton.

This letter has the sound of French u, Latin and Old English y; and it is transliterated in English as u or y.

You can see all of the letters of the Greek Alphabet on this page.