• IPA: /taʊ/, /tɔː/

tau (plural taus)

  1. The letter Τ/τ in the Greek, Hebrew and ancient Semitic alphabets, being the nineteenth letter of the Classical and Modern Greek, the twenty-first letter of Old and Ancient Greek.
  2. A Τ-shaped sign or structure; a Saint Anthony's cross, sometimes regarded as a sacred symbol.
    • 1658: Nor shall we take in the mysticall Tau, or the Crosse of our blessed Saviour, which having in some descriptions an Empedon or crossing foot-stay, made not one single transversion. — Sir Thomas Browne, The Garden of Cyrus (Folio Society 2007, p. 168)
  3. (particle, dated) A tau meson, now usually known as a kaon.
  4. (particle) An unstable heavy lepton, which decays into a muon or electron; a tauon.
  5. (biology) Tau protein, a type of protein that stabilizes microtubules in the human central nervous system, failures of which are associated with forms of dementia.
    • 1999, Matt Ridley, Genome, Harper Perennial 2004, p. 263:
      Quite what that job is remains obscure, but one theory is that it is to stabilise another protein called tau, which is supposed in turn to keep in shape the tubular ‘skeleton’ of a neuron.
  6. (finance) A measurement of the sensitivity of the value of an option to changes in the implied volatility of the price of the underlying asset.
  7. (mathematics, neologism) An irrational and transcendental constant representing the ratio of the circumference of a Euclidean circle to its radius, approximately 6.2831853071; equal to twice the value of pi. Often written τ.
  • (measure of derivative price sensitivity) kappa, vega
  • French: tau
  • German: Tau
  • Italian: tau
  • Portuguese: tau
  • Russian: та́у
  • Spanish: tau
  • French: croix en tau, croix de Saint-Antoine
  • German: Taukreuz, Antoniuskreuz, Antoniterkreuz, Ägyptisches Kreuz, Plattkreuz (heraldry)

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