Definition of upsilon in English:


Pronunciation /ˈʊpsɪlɒn//ˈjuːpsɪlɒn//juːpˈsʌɪlən//ʌpˈsʌɪlən/


  • 1The twentieth letter of the Greek alphabet (Υ, υ), transliterated as ‘u’ or (chiefly in English words derived through Latin) as ‘y’.

    • ‘Look lower down the alphabet - theta perhaps, or even upsilon.’
    • ‘Typesetters typically confuse Greek letters in setting Greek quotations: nu with upsilon, theta with phi.’
    1. 1.1Astronomy followed by Latin genitive The twentieth star in a constellation.
      ‘Upsilon Scorpii’
      • ‘The discovery comes only seven months after the first multi-planet system outside our own, around the star Upsilon Andromedae, was identified.’
      • ‘For example, Upsilon Andromedae is now known to possess a system of three large planets.’
      • ‘The system they focused on, three huge Jupiter-like planets orbiting the central star Upsilon Andromedae, was the first extrasolar multi-planet system ever discovered by Doppler spectroscopy.’
    2. 1.2Physics A meson thought to contain a b quark bound to its antiparticle, produced in particle accelerators.
      • ‘Some colleagues were surprised that he had not won a Nobel earlier, perhaps for the discovery in 1977 of the upsilon particle, the most massive nuclear particle yet found.’
      • ‘The total energy of the muon pair corresponds to the mass of the upsilon particle, while the two jets appear to have come from the decay of a Z particle, carrier of the weak force.’
      • ‘The new phenomena included major breakthroughs in physics, including the discovery of the upsilon particle, or bottom quark, in 1977.’
      • ‘About eight times the mass of a proton, the zeta particle was created when electrons and positrons collided at about 10 Gev (gigavolts of energy), where it appeared among the decay products of the upsilon particle.’
      • ‘Similarly, the bottom quark was inferred from the discovery of the upsilon particle by Leon Lederman in 1977 at Fermilab.’
      • ‘The upsilon particle is a meson which was discovered at Fermilab in 1977.’
      • ‘Use of the tracking information told the energies and momenta of the muons - which could then be traced back to find the new upsilon particle and its mass.’


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.