Omicron
Omicron (Ο, ο) is the 15th letter of the Greek alphabet, a short o. Since November 2021 it is also the World Health Organization’s name for the SARS-CoV-2 variant B.1.1.529.
How to read it
The name means “small o”, from the Greek ō mikrón (Dictionary.com); Omega is “great o”. Dictionary.com gives the American pronunciation as OM-i-kron or OH-mi-kron, and the Cambridge Dictionary gives British English oh-MY-kron /əʊˈmaɪ.krɒn/. The Collins English Dictionary describes it as a short vowel, transliterated as o. The letter looks exactly like the Latin O and o, but Unicode codes them separately.
Also searched as: omicron letter, omicron symbol, ο, Ο.
Capital and small forms
| Form | Character | Code point | Unicode name |
|---|---|---|---|
| Capital | Ο | U+039F | GREEK CAPITAL LETTER OMICRON |
| Small | ο | U+03BF | GREEK SMALL LETTER OMICRON |
The Latin O is U+004F and o is U+006F.
Omicron and big-O notation
The O of big-O notation in computer science looks like an omicron, but MIT’s algorithms course calls it “big-Oh” notation, and the notation uses the symbols O, Θ and Ω.
The Omicron variant
The WHO began giving key SARS-CoV-2 variants simple Greek-letter labels in May 2021. B.1.1.529 was first reported to the WHO from South Africa on 24 November 2021, and on 26 November the WHO designated it a variant of concern, named Omicron. CNN reported that the WHO skipped Nu and Xi, the two letters before it.
Write in Greek letters
stringmash.comGreek alphabet translatorWrite English in Greek letters by sound, or turn Greek back into Latin letters as Greek passports do.Read next
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More greek letters
The same shape elsewhere
Browse symbols drawn with circles or letters and numbers.
Sources
- omicron (Dictionary.com entry), Dictionary.com Unabridged; Collins English Dictionary, Dictionary.com, Entry, American and British (Collins) senses
- omicron (Cambridge Dictionary entry), Cambridge Advanced Learner’s Dictionary, Cambridge University Press, Entry
- Greek and Coptic: Range 0370–03FF (code chart), The Unicode Standard, Version 18.0, Unicode Consortium, Greek capital and small letters
- C0 Controls and Basic Latin: Range 0000–007F (code chart), The Unicode Standard, Version 18.0, Unicode Consortium, Basic Latin
- 6.006 Recitation 1 Notes: Asymptotic Complexity, MIT OpenCourseWare, Fall 2011, Massachusetts Institute of Technology, p. 1
- Classification of Omicron (B.1.1.529): SARS-CoV-2 Variant of Concern, Statement, 26 November 2021, World Health Organization, Statement
- Tracking SARS-CoV-2 variants, World Health Organization, Background
- Why WHO skipped two letters of the Greek alphabet in naming Omicron, 29 November 2021, CNN, Article
Researched, edited and approved by Rory Hansen before publishing. Last reviewed September 30, 2026. How we research
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