sigma — English Dictionary

Noun

1. The eighteenth letter of the Classical and Modern Greek alphabets (Σ, σ), the twentieth letter of Old and Ancient.

   Examples

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   Their names, which are expressive of some bodily or mental excellence, all end with the same letter---the letter which is called San by the Dorians, and Sigma by the Ionians.

2. The symbol Σ, used to indicate summation of a set or series.

3. The symbol σ, used to indicate one standard deviation from the mean, particularly in a normal distribution.

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   2011, Paul Rincon, (bbc.co.uk) LHC: Higgs boson 'may have been glimpsed' None of the spikes seen by the experiments is at much more than the "two sigma" level of certainty. A level of "five sigma" is required to claim a discovery, meaning there is less than a one in a million chance the data spike is down to a statistical fluke.

4. A sigma male (a self-reliant and assertive male).

   Usage

   • Internet

Adjective

1. Possessing characteristics of a sigma male.

   Usage

   • Internet

Noun

1. the 18th letter of the Greek alphabet

   Broader terms

   letterletter of the alphabetalphabetic character