Definitions

from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. The 18th letter of the Greek alphabet. See Table at alphabet.
  • n. A sigma factor.
  • n. A sigma baryon.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. The name for the eighteenth letter of the Classical and Modern Greek, the nineteenth letter of Old and Ancient.
  • n. The symbol Σ, used to indicate summation of a set or series.
  • n. The symbol σ, used to indicate one standard deviation from the mean, particularly in a normal distribution.

from the GNU version of the Collaborative International Dictionary of English

  • n. The Greek letter Σ, σ, or ς (English S, or s). It originally had the form of the English C.

from The Century Dictionary and Cyclopedia

  • n. The name of the Greek letter Σ, σ, ς, equivalent to the English S, s. (For its early forms, see under S.)
  • n. An S-shaped or sigmoid flesh-spicule of a sponge.
  • n. The curve of the letter S or any approximate curve.
  • n. In descriptive biol., one of the S-shaped ridges on the surface of certain molluscan shells, as those of gastropods and cephalopods.
  • n. In experimental psychology, the time-unit, of a second: abbreviated σ.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. the 18th letter of the Greek alphabet

Etymologies

Greek sīgma, of Phoenician origin; see smk in Semitic roots.
(American Heritage® Dictionary of the English Language, Fourth Edition)

Examples

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