# sigma

> English word · Noun · IPA /ˈsɪɡmə/ · frequency rank #14,835

## Definitions
1. The eighteenth letter of the Classical and Modern Greek alphabets (Σ, σ), the twentieth letter of Old and Ancient.
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.
4. A sigma male (a self-reliant and assertive male).

## Etymology
From Ancient Greek σῖγμα (sîgma), probably from the root σῑγ- (sīg-) as seen in σίζω (sízō, “to hiss”) + -μα (-ma, nominal suffix).

## Easily confused with
- **SIM** (https://plainspell.com/en/vs/sigma-vs-sim)
- **SMA** (https://plainspell.com/en/vs/sigma-vs-sma)
- **sign** (https://plainspell.com/en/vs/sigma-vs-sign)
- **Sims** (https://plainspell.com/en/vs/sigma-vs-sims)
- **soma** (https://plainspell.com/en/vs/sigma-vs-soma)
- **Sina** (https://plainspell.com/en/vs/sigma-vs-sina)
- **simi** (https://plainspell.com/en/vs/sigma-vs-simi)
- **Sita** (https://plainspell.com/en/vs/sigma-vs-sita)
- **Suga** (https://plainspell.com/en/vs/sigma-vs-suga)
- **signs** (https://plainspell.com/en/vs/sigma-vs-signs)
- **silva** (https://plainspell.com/en/vs/sigma-vs-silva)
- **Simms** (https://plainspell.com/en/vs/sigma-vs-simms)
- **Sinha** (https://plainspell.com/en/vs/sigma-vs-sinha)
- **summa** (https://plainspell.com/en/vs/sigma-vs-summa)
- **Sitka** (https://plainspell.com/en/vs/sigma-vs-sitka)
- **signal** (https://plainspell.com/en/vs/sigma-vs-signal)
- **stigma** (https://plainspell.com/en/vs/sigma-vs-stigma)
- **sig** (https://plainspell.com/en/vs/sig-vs-sigma)
- **sia** (https://plainspell.com/en/vs/sia-vs-sigma)
- **sigh** (https://plainspell.com/en/vs/sigh-vs-sigma)

## Common misspellings (7)
`isgma`, `sgima`, `sigam`, `siggma`, `sigmma`, `simga`, `ssigma`

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/sigma