tau
/taʊ/
"tau" is a 3-letter English headword indexed on PlainSpell.
The verdict
“tau” is a moderately-common English word, ranked #19,983 in English word frequency and used as a noun.
- #19,983
- frequency rank, English
- 3
- letters
- 20
- confusable pairs
According to Wiktionary data (CC BY-SA, analyzed May 6, 2026) - 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.
Visual similarity to commonly confused words
How many letter changes separate each confused pair (Levenshtein distance, normalized).
Source: PlainSpell confusable corpus (Wiktionary, CC BY-SA).
| Property | Value |
|---|---|
| Headword | tau |
| Language | English |
| Part of speech | Noun |
| IPA | /taʊ/ |
| Letters | 3 |
| Frequency rank | #19,983 |
| Misspellings tracked | 0 |
| Confusable pairs | 20 |
| Source | Wiktionary (kaikki.org) |
Where “tau” sits in English frequency
Spelling & Dictionary Insight
The English entry for tau is 3 letters long, classified as a noun, and transcribed in the International Phonetic Alphabet as /taʊ/. Corpus data places it at rank #19,983 in overall English word frequency, marking it as uncommon enough that many writers pause before typing it. Wiktionary records 11 distinct senses for this headword, so context determines which meaning a reader should apply.
Our edit-distance generator produced no likely misspellings for tau, a straightforward case of a spelling with little room for common typos. It also participates in 20 confusable-pair relationships, "to", "TV", "te", and more, since the words sound or look close enough that writers reach for the wrong one mid-sentence.
Etymologically, the entry records: 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 … The correct English form is tau, spelled T-A-U.
Definition
- 1The 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.
- 2Alternative form of taw; the 22nd and last letter of many Semitic alphabets/abjads, including Phoenician, Aramaic, Hebrew, Syriac, and Arabic.
- 3A Τ-shaped object or sign; a Saint Anthony's cross, sometimes regarded as a sacred symbol.
- 4A Τ-shaped object or sign; a Saint Anthony's cross, sometimes regarded as a sacred symbol.
- 5The ankh symbol (☥).
- 6Chiefly written τ: used to designate the nineteenth star (usually according to brightness) in a constellation.
- 7A measurement of the sensitivity of the value of an option to changes in the implied volatility of the price of the underlying asset.
- 8Chiefly 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).
- 9Ellipsis 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”).
- 10Chiefly written τ.
- 11Chiefly written τ.
Etymology
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.
This word in other languages
Definitions, pronunciation, and etymology for this entry are drawn from Wiktionary via the kaikki.org structured extract (CC BY-SA); frequency ordering uses the FrequencyWords open word-frequency list (2018 English corpus, MIT). See the methodology for how each field is sourced and updated.
Frequently Asked Questions
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Using “tau”
The practical upshot for anyone who landed here from a spell-check.
- The one correct English spelling is T-A-U - every other letter order is a misspelling in standard orthography.
- Say it as /taʊ/ (IPA); tap the speaker on the pronunciation badge to hear it where audio exists.
- Don't mix it up with “to” - see the side-by-side comparison. tau vs to
- Browse more English words and confusable pairs in the same reference. English words
Data Source
Wiktionary (via kaikki.org), licensed under CC BY-SA & GFDL. Word ordering uses an open word-frequency list; misspelling variants are generated by edit-distance from the correct headword.