tau

noun10

1. •
   The letter Τ /τ in the Greek alphabet; being the nineteenth letter of the Classical and Modern Greek, and the twenty-first letter of the Old and Ancient Greek alphabets.
2. •
   Ellipsis of tau protein (“a protein abundant especially in the neurons of the human central nervous system that stabilizes microtubules, and when misfolded is associated with forms of dementia such as Alzheimer's and Parkinson's diseases”).

   • 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. — 1999
3. •
   Chiefly written τ: an irrational and transcendental constant representing the ratio of the circumference of a Euclidean circle to its radius, equal to twice the value of pi (2π; approximately 6.2831853071).
4. •
   Ellipsis of tau lepton or tau particle (“an unstable elementary particle which is a type of lepton, having a mass almost twice that of a proton, a negative charge, and a spin of ½; it decays into hadrons (usually pions) or other leptons, and neutrinos; a tauon”).
5. •
   A Τ-shaped object or sign; a Saint Anthony's cross, sometimes regarded as a sacred symbol.

   • 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. — 1658
6. •
   A crosier with a Τ-shaped head.
7. •
   A measurement of the sensitivity of the value of an option to changes in the implied volatility of the price of the underlying asset.

   • (includes a list of coordinate terms)
8. •
   Chiefly written τ: used to designate the nineteenth star (usually according to brightness) in a constellation.
9. •
   The ankh symbol (☥).
10. •
    (historical) Ellipsis of tau meson, now known as a kaon.

noun1

1. •
   Abbreviation of treatment as usual.