View source for Τ

{{also|Τ|τ.|τ'|Appendix:Variations of "t"}}
{{character info}}
{{character info/var|𝜏}}

==Translingual==
[[File:2pi-unrolled.gif|thumb|When a circle's [[radius]] is 1 unit, its circumference is τ units.]]

===Symbol===
{{head|mul|symbol|head={{serif|τ}}}}

# {{lb|mul|physics}} [[torque|Torque]].
# {{lb|mul|physics}} [[shear stress|Shear stress]].
# {{lb|mul|physics}} [[optical depth|Optical depth]].
#* {{quote-journal|en|year=2006|month=August|author=Alexander V. Krivov; Artem G. Feofilov; Valeri V. Dikarev|title=Search for the putative dust belts of Mars: The late 2007 opportunity|journal=w:Planetary and Space Science|volume=54|issue=9–10|page=871|doi=10.1016/j.pss.2006.05.007|passage=The first one was made by the Viking Orbiter 1 spacecraft in 1980 (Duxbury and Ocampo, 1988) and brought a negative result, setting the upper limit of the normal optical depth of the putative tori to <math>\tau \lesssim 3 \times 10^{-5}</math>.}}
# {{lb|mul|mathematics|neologism}} An [[irrational]] [[constant]] defined as the [[ratio]] of the [[circumference]] of a [[circle]] to its [[radius]], equal to the [[radian]] measure of a [[full]] {{l|en|turn|id=geometry}}; approximately 6.283185307 (equal to 2π, or twice the value of [[π]]).
# {{lb|mul|particle}} [[tauon]]
# {{lb|mul|{{w|Teutonista}}}} a voiceless dental plosive (IPA [[t̪|{{IPAfont|[t̪]}}]]).
# {{lb|mul|UPA}} A [[voiced]] [[coronal]] [[click]] consonant (dental {{angbr|[[τ̦]]}} = IPA {{IPAfont|[ɡ͜ǀ]}}; [[cacuminal]] {{angbr|[[τ̣]]}} = IPA {{IPAfont|[ɡ͜ǃ]}}).

===See also===
* {{pedia}}

==Ancient Greek==

===Etymology===
Derived from its [[majuscule]] counterpart [[Τ]].

===Letter===
{{head|grc|letter|lowercase||uppercase|Τ}}

# Lower-case [[tau]] ({{l|grc|ταῦ|tr=-}}), the 19th letter of the ancient [[Greek alphabet]]. It represented the [[voiceless]] [[unaspirated]] [[w:voiceless alveolar plosive|alveolar or dental plosive]] {{IPAchar|/t/}}. It is preceded by [[σ]] and followed by [[υ]].

====Derived terms====
See also [[tau]]
* {{l|el|τ΄}}, {{l|el|͵τ}}
* {{l|mul|т|sc=Cyrl}}, {{l|mul|Т|sc=Cyrl}} {{qualifier|[[Cyrillic]]}}
* {{l|got|𐍄|tr=-}} {{qualifier|[[Gothic]]}}
* {{l|cop|ⲧ|sc=Copt|tr=-}}, {{l|cop|Ⲧ|sc=Copt|tr=-}} {{qualifier|[[Coptic]]}}

===See also===
* {{Grek-script}}

==Greek==

===Letter===
{{head|el|letter|lowercase||uppercase|Τ}}

# The [[lower case]] letter [[tau]] ([[ταυ]]), the 19th letter of the modern [[w:Greek alphabet|Greek alphabet]].

===See also===
{{Grek-script}}
* {{l|el|τ΄}}
* {{l|el|͵τ}}