Definition of tau in English:


Pronunciation /taʊ//tɔː/


  • 1The nineteenth letter of the Greek alphabet (Τ, τ), transliterated as ‘t’.

    • ‘It originated as the Phoenician symbol taw, which the Greeks adopted and adapted as tau, which was in turn adopted by the Etruscans and then the Romans as T.’
    • ‘Eqs. 3-5 are characterized by three parameters, namely sigma 0, tau, and alpha.’
    • ‘For example, in the modern version, beta is veta or vita; delta is thelta; zeta is zita; eta is ita; theta is thita; lambda is lamvtha; tau is taf.’
    • ‘Alpha, rho, tau, sigma, omega, Ash went over the letters he saw in his mind while Lari just stared, apparently in her own little world.’
    1. 1.1Astronomy followed by Latin genitive The nineteenth star in a constellation.
      ‘Tau Ceti’
      • ‘It is another spacecraft, an interstellar explorer that charted the Tau Ceti and Epsilon Indi systems in the mid-twenty-second century.’
      • ‘Sitting in high orbit over New Edinburgh in the Tau Ceti system, watching the rings of the planet slowly spin beneath me was breath-taking.’
      • ‘This newly discovered planet orbits a star called Tau Gruis, which is about 100 light-years away.’
      • ‘The most likely destinations are the stars closest to Earth, such as Alpha Centauri and Proxima Centauri, Tau Ceti, and Epsilon Eridani.’
      • ‘Team member Mark Wyatt says the reasons for the huge number of comets orbiting Tau Ceti are not fully understood.’
    2. 1.2Physics An unstable subatomic particle of the lepton class, with a charge of −1 and a mass roughly 3,500 times that of the electron.
      • ‘SLAC physicists have won three Nobel prizes for discoveries of quarks and an elementary particle called the tau lepton, known today as fundamental building blocks of matter.’
      • ‘Even at the deepest level we know, of elementary particles, charge seems to be an integral part of the particles, quarks (which form protons and neutrons, and other heavy particles) are charged, and so are electrons, muons, and taus.’
      • ‘They want to know why the neutrinos seem to have masses so much smaller than those of other members of their class of fundamental particles, which includes electrons and their heavy cousins, muon and tau particles.’
      • ‘The electron is also joined by two more massive cousins - the muon and tau leptons - and each of these also has a corresponding neutrino.’
      • ‘Scientists became alerted to the existence of the third, tau neutrino in 1977 with the discovery of the tau lepton.’