sigma

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sigma

1. the 18th letter in the Greek alphabet (Σ, σ or, when final, ς), a consonant, transliterated as S
2. Maths the symbol Σ, indicating summation of the numbers or quantities indicated

sigma

(σ) The 18th letter of the Greek alphabet, used in stellar nomenclature usually to designate the 18th-brightest star in a constellation or sometimes to indicate a star's position in a group.

sigma

[′sig·mə]
(invertebrate zoology)
A C-shaped spicule.

portico

1. A covered entrance whose roof is supported by a series of columns or piers, commonly placed at the front entrance to a building.
2. A stoa.

SIGMA

A scientific visual programming environment from NASA.

http://fi-www.arc.nasa.gov/fia/projects/sigma/.