Learn how to say Upsilon correctly in English with this tutorial pronunciation video.
Oxford dictionary definition of the word upsilon:
the twentieth letter of the Greek alphabet (Υ, υ), transliterated as ‘u’ or (chiefly in English words derived through Latin) as ‘y’.
(Upsilon) [followed by Latin genitive] Astronomy the twentieth star in a constellation:
(also upsilon particle) Physics a meson thought to contain a b quark bound to its antiparticle, produced in particle accelerators.
Greek, literally ‘slender U’, from psilos ‘slender’, referring to the need to distinguish upsilon from the diphthong oi: in late Greek the two had the same pronunciation