Sigma

How to spell sigma

5 letters · 2 syllables

How to pronounce sigma

Say the part in capitals loudest.

What does sigma mean?

1. nounThe eighteenth letter of the Greek alphabet, written Σ or σ.

Sigma in a sentence

• The upper-case sigma is used in maths to mean the sum of a series.

• In his lecture notes the lower-case sigma stood for the standard deviation.

Where does sigma come from?

Language of origin: Greek

Sigma is the name of the eighteenth letter of the Greek alphabet, written as Σ in upper case and σ (or ς at the end of a word) in lower case. The Greeks themselves took the letter from the Phoenician character shin, which represented an 's' sound, and the Greek name 'sigma' may derive from a verb meaning 'to hiss', a fitting label for a sibilant sound. The letter passed into the vocabulary of English-speaking mathematicians and scientists, who adopted the capital Σ as the standard symbol for summation and the lower-case σ to denote standard deviation in statistics. Because of its statistical role, the word now also turns up in business jargon such as 'Six Sigma', a quality-control method named for striving to keep defects within six standard deviations of the mean. The spelling stays close to its Greek source, and the silent-feeling 'g' before 'm' is the small detail most likely to trip a writer.

How the word is built

• sigma (from Greek sigma, the eighteenth letter of the Greek alphabet; treated as a single root with no affixes)