Added 9 October 2026
tau
/taʊ/ symbol
Latin root: tau Coined: 1927, by Martin Lewis Perl Wiktionary
symbol Definition from Wiktionary (CC BY-SA). Pronunciation from Wiktionary, via Kaikki.org. More about tau at Wordnik → Where our words come from →
noun
- 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.
- Alternative form of taw; the 22nd and last letter of many Semitic alphabets/abjads, including Phoenician, Aramaic, Hebrew, Syriac, and Arabic.
- A Τ-shaped object or sign; a Saint Anthony's cross, sometimes regarded as a sacred symbol. A crosier with a Τ-shaped head.
Origin
From Middle English tau, taue, from Latin tau, from Ancient Greek ταῦ (taû) and Hebrew תָּו (tav). Sense 7 was used by Joseph M. Lindenberg in 1991, and popularized by the American educator and entrepreneur Michael Hartl in a 2010 paper which explains that τ resembles π; and that τ is the Greek equivalent of t, the first letter of turn, and 2π corresponds to one turn of a circle with a radius of one unit. Sense 8.1 (“ellipsis of tau lepton or tau particle”) was coined by the American physicist Martin Lewis Perl (1927–2014) after the first letter of Ancient Greek τρίτον (tríton, “third”), since the tau lepton or tauon was the third charged lepton discovered.
From Wiktionary, via Kaikki.org (CC BY-SA)