Definition of sigma in English:

sigma

Syllabification: sig·ma
Pronunciation: /ˈsigmə
 
/

noun

  • 1The eighteenth letter of the Greek alphabet (Σ, σ), transliterated as ‘s.’.
    • The form ς is used instead of σ at the end of a word. The uncial form, called lunate sigma and resembling the letter C, is also sometimes used
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    • He coined this latter term and employed the Greek letter lower case sigma to denote its population parameter.
    • Alpha, rho, tau, sigma, omega, Ash went over the letters he saw in his mind while Lari just stared, apparently in her own little world.
    • Finally, even if epsilon is the correct reading, in the letter space to its right, where Meritt read part of an iota, are traces of what appears to be a sigma.
  • 2 (Sigma) [followed by Latin genitive] Astronomy The eighteenth star in a constellation: Sigma Octantis
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    • Finally, the final green beam of light was shot straight up at the constellation Sigma.
  • 3 Chemistry & Physics Relating to or denoting an electron or orbital with zero angular momentum around an internuclear axis.
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    • These conical intersections are fundamentally different from the ‘H-vinyl’ structures found in simple alkenes because they involve the interaction of four sigma electrons, as opposed to two pi electrons and two sigma electrons.
    • The sigma bond occupies the internuclear space, and the two pi bonds are at 90° angles to each other surrounding the carbon-carbon internuclear space.
    • The triple bond is composed of one sigma bond from overlap of sp hybrid orbitals, and two pi bonds, from overlap of two sets of p orbitals.

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  • 1 (Σ) Mathematical sum.
  • 1.1 (σ) Standard deviation.

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