• synonyms


  1. the 18th letter of the Greek alphabet: Σ, σ, ς.
  2. the consonant sound represented by this letter.
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Origin of sigma

1600–10; < Latin < Greek sígma
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

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British Dictionary definitions for 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
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Word Origin

Greek, of Semitic origin; related to Hebrew samekh
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for sigma

18th letter of the Greek alphabet, corresponding to Latin S, a metathesis of Hebrew samekh. In uncial writing, shaped like an S or a C.

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Online Etymology Dictionary, © 2010 Douglas Harper

sigma in Medicine


  1. The 18th letter of the Greek alphabet.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

sigma in Science


  1. A sigma baryon.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.