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.

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.