sigma

noun

sig·​ma ˈsig-mə 

1

: the 18th letter of the Greek alphabet see Alphabet Table

2

: standard deviation

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Slang Meaning of Sigma

Sigma is now also used to mean “a coolly independent, successful man.” Learn more >

Examples of sigma in a Sentence

Recent Examples on the Web

The confidence level ranges from 2.8 to 4.2 sigma, depending on the combination of datasets—just shy of the five-sigma threshold. —Jennifer Ouellette, Ars Technica, 19 Mar. 2025

In the following years, the Hungarian team has built up an impressive list of accomplishments, all of which point to the reality of this new particle, including statistical significance of over 6 sigma, and work with collaborators to find similar signals. —Paul Sutter, Space.com, 24 Dec. 2024

According to the group’s calculations, the Planck data point to a closed universe with a standard deviation of 3.5 sigma (a statistical measurement that means about 99.8% confidence that the result isn’t due to random chance). —Rafi Letzter, Scientific American, 5 Nov. 2019

Thomson and his team must reach five-sigma certainty to definitively claim a discovery. —Quanta Magazine, 14 May 2015

Historically, most industrial companies operate between three and four sigma, making them between 93% and 99.3% defect-free (these figures can vary slightly depending on the statistical model). —Oliver Staley, Quartz at Work, 3 Sep. 2019

The gold standard for discovery is a five-sigma result, comparable to tossing 21 heads in a row. —Jennifer Ouellette, Quanta Magazine, 18 July 2013

Typically, only five sigma is needed to call something a discovery. —John Timmer, Ars Technica, 28 June 2018

Physicists and astronomers, however, aren't usually convinced that two phenomena are connected until there's no more than a one in 3.5 million, or 5 sigma, probability of a coincidence. —Daniel Clery, Science | AAAS, 12 July 2018

Word History

Etymology

Greek

First Known Use

1584, in the meaning defined at sense 1

Rhymes for sigma

• stigma
• enigma
• kerygma

Kids Definition

sigma

noun

sig·​ma ˈsig-mə 

: the 18th letter of the Greek alphabet

—Σ or σ or ς