The eighteenth letter of the Classical and Modern Greek alphabets, the twentieth letter of Old and Ancient. / (mathematics) The symbol Σ, used to indicate summation of a set or series.

plural of sigma

(chemistry) A covalent atomic bond that is rotationally symmetric about its axis.

plural of lunate sigma

The form of the Greek letter sigma used in Medieval Greek and occasionally in Greek Orthodox Church transcriptions: ϲ.

plural of final sigma

The form of the Greek letter sigma only ever used as the last letter of a word: ς.

(mathematical analysis) Alternative form of σ-additivity

plural of sigma bond

a set of techniques and tools for process improvement.