sigma

sigma — noun

1. The 18th character in the Greek writing system, written as Σ (uppercase) or σ an

1.nounB1
Definition

The 18th character in the Greek writing system, written as Σ (uppercase) or σ and ς (two lowercase forms).

Example

Mauricio learned to write the letter sigma in his Ancient Greek class.

letter name in language-learning context

In maths, the capital sigma (Σ) means you should add up all the terms.

capital Σ for summation in mathematics

Common collocations
  • capital sigma
  • lowercase sigma
  • final sigma
  • sigma symbol
  • letter sigma
  • sigma notation
  • sigma bond
  • Six Sigma

Grammar Patterns

sigma + [verb]

the letter sigma

Usage Note

Sigma has two lowercase forms depending on position in a word: σ (medial, used everywhere except the end) and ς (final, used only at the end of a word). This distinction matters when writing Greek text. Outside of Greek-language contexts, sigma is most often seen in mathematical notation (Σ for summation) and statistics (σ for standard deviation).

Common Mistakes

I wrote ς in the middle of the Greek word.
I wrote σ in the middle of the Greek word.
The form ς (final sigma) is only used at the end of a word; σ is used in all other positions.

Word family

  • sigmoid
    adjectiveC2

Synonym discussion

Sense: noun/1

Alpha, beta, pi, and sigma are all letters of the Greek alphabet, but they appear in different kinds of contexts. Alpha (α) and beta (β) are the first two letters and are commonly used in science to label versions (alpha version, beta test). Pi (π) is famous in mathematics for representing the ratio of a circle's circumference to its diameter (3.14...). Sigma (σ/Σ) is unique among these because of its two lowercase forms and because its capital form (Σ) is used as a summation symbol. Learners who already know alpha and beta will find sigma easy to remember — it comes after rho and before tau in the alphabet order.

alpha ↗beta ↗pi ↗

Common collocations

Nouns

  • sigma notation
  • sigma bond
  • sigma factor
  • Six Sigma

Phrases

  • written as sigma
  • known as sigma
  • the letter sigma

Etymology

PhoenicianGreekLatinEnglish

The English name 'sigma' comes directly from the Greek σίγμα (sígma), the name of the 18th letter. The Greek letter itself was adapted from the Phoenician letter 𐤔 (shin), which originally meant 'tooth' and represented the 'sh' sound. The Greeks repurposed it for the 's' sound and gave it the name sigma. The word entered English in the 16th century through Latin and was first used in mathematical and theological writings.