[ tou, taw for 1, 2, 4; tahv, tawv for 3 ]
/ taʊ, tɔ for 1, 2, 4; tɑv, tɔv for 3 /


the 19th letter of the Greek alphabet (T, τ).
the consonant sound represented by this letter.
Also tau·on [tou-on] /ˈtaʊ ɒn/. Physics. tau lepton.
Also called tau protein. Biochemistry. a protein that is an important component of nerve cells, helping to maintain their function and structure: in the brain, distortions in the protein’s molecular shape is associated with the onset of Alzheimer’s disease.

Origin of tau

1250–1300; Middle English < Latin < Greek taû < Semitic; cf. tav
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for tau

British Dictionary definitions for tau


/ (tɔː, taʊ) /


the 19th letter in the Greek alphabet (Τ, τ), a consonant, transliterated as t

Word Origin for tau

C13: via Latin from Greek, of Semitic origin; see tav
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for tau


nineteenth letter of the Greek alphabet, from Hebrew taw, last letter of the Hebrew alphabet, literally "sign, mark."

Online Etymology Dictionary, © 2010 Douglas Harper

Medicine definitions for tau



The 19th letter of the Greek alphabet.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.