tau

1. A Τ-shaped object or sign; a Saint Anthony's cross, sometimes regarded as a sacred symbol.

2. (astronomy) Chiefly written τ: used to designate the nineteenth star (usually according to brightness) in a constellation.

3. (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.Examples: "(includes a list of coordinate terms)"Synonyms: kappa, vega

4. (mathematics, neologism) 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).neologism

5. (neurology) 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”).Examples: "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."abbreviationalt-ofellipsis

6. (particle physics) Chiefly written τ.abbreviationalt-ofellipsisparticle