Number & MeasureGreek → English
Sigma
/ˈsɪɡmə/noun
The eighteenth letter of the Greek alphabet, used for summation and for standard deviation.
The Greek roots
σίγμα
sígma
the letter s
Literally: “the letter s”
Follow a root:σίγμα1 word
The story of the word
The letter name came with the alphabet from Phoenician, and the Greeks themselves offered no convincing account of it. All its modern weight is borrowed: Euler used capital Σ for a sum in the eighteenth century, and Karl Pearson fixed lower-case σ as the standard deviation in the 1890s. That second choice is why a manufacturing programme could be sold as six sigma, and why the sigmoid colon is named for a letter's curve.
- How it travelled
- Phoenician → Ancient Greek → English
Same family
sigmoidsigmoidoscopysigmatism
In a sentence
A result three sigma from the mean is interesting; five sigma is a discovery.