# sigma

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## σ

,**Σ**

**1.**The 18th letter of the Greek alphabet, sigma.

**2.**(σ) Symbol for reflection coefficient; standard deviation; a factor in prokaryotic RNA initiation; wavenumber; surface tension.

**3.**(Σ) Summation of a series.

## sig·ma

(sig'mă),The 18th letter of the Greek alphabet, σ.

## sigma

(sĭg′mə)*n.*

A sigma factor.

**sig′mate′**(-māt′)

*adj.*

## sigma

[sig′mə]

Σ, σ, and s, the eighteenth letter of the Greek alphabet.

## σ

Abbreviation for standard deviation; reflection coefficient.

## sig·ma

**(σ,Σ)**(sig'mă)

**1.**The 18th letter of the Greek alphabet.

**2.**(σ)

**reflection coefficient;**

**standard deviation;**a factor in prokaryotic RNA initiation; surface tension

**3.**(Σ) Summation of a series.

## sig·ma

(sig'mă)**1.**The 18th letter of the Greek alphabet (σ, Σ).

**2.**(σ) reflection coefficient; standard deviation; a factor in prokaryotic RNA initiation; surface tension

**3.**(Σ) Summation of a series.

## sigma

the Greek letter σ or σ; the former frequently denotes a standard deviation, the latter is used in mathematics for the sum of the values of the term nominated.

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