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[ep-suh-lon, -luh n or, esp. British, ep-sahy-luh n] /ˈɛp səˌlɒn, -lən or, esp. British, ɛpˈsaɪ lən/
the fifth letter of the Greek alphabet (E, ε).
the consonant sound represented by this letter.
Mathematics. an arbitrarily small quantity, used to indicate that a given quantity is small, or close to zero.
Origin of epsilon
< Greek è psīlón bare, simple e (as opposed to diphthongal spellings which in later Gk represented the same sound) Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the Web for epsilon
Historical Examples
  • Next look at epsilon (ε), and you will find near it two seventh-magnitude companions, making a beautiful little triangle.

    Astronomy with an Opera-glass Garrett Putman Serviss
  • A pilot comes back from epsilon Eridani, for example, and insists on giving everybody left-handed salutes.

    Next Door, Next World Robert Donald Locke
  • The fact still remains that epsilon had better be habitable or Pan-Asia will scream we're hogging it.

    Competition James Causey
  • The most southerly star in this pentagon is known as epsilon Botes and is one of the finest double stars in the heavens.

    Astronomy for Young Folks Isabel Martin Lewis
  • Turn your glass upon the star shown in the map just above Mu (μ) and epsilon (ε).

    Astronomy with an Opera-glass Garrett Putman Serviss
  • epsilon Lyr, which is the northern one of these two stars, may be used as a test of keen eyesight.

    Astronomy for Young Folks Isabel Martin Lewis
  • And goeth from epsilon down to Mu: the reference is to some numbering on the parchment.

  • Reaching the hottest of all—epsilon Orionis and two stars in Argo—hydrogen is predominant, with traces of a few metals and carbon.

    Man's Place in the Universe Alfred R. Wallace
  • I dreamed they all committed suicide because epsilon was too good for them.

    Competition James Causey
  • Other airships, the Delta and epsilon, of increased size and engine-power, were designed between 1911 and 1913.

    The War in the Air; Vol. 1 Walter Raleigh.
British Dictionary definitions for epsilon


/ˈɛpsɪˌlɒn; ɛpˈsaɪlən/
the fifth letter of the Greek alphabet (Ε, ε), a short vowel, transliterated as e
Word Origin
Greek e psilon, literally: simple e


/ˈɛpsɪˌlɒn; ɛpˈsaɪlən/
(foll by the genitive case of a specified constellation) the fifth brightest star in a constellation: Epsilon Aurigae
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
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Word Origin and History for epsilon

from Greek, literally e psilon "bare -e-, -e- and nothing else," in contradistinction to the diphthong -ai-, which has the same sound. Greek psilon "smooth, simple" is of uncertain origin.

Online Etymology Dictionary, © 2010 Douglas Harper
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epsilon in Medicine

epsilon ep·si·lon (ěp'sə-lŏn', -lən)

  1. Symbol ε The fifth letter of the Greek alphabet.

  2. The fifth in a series.

  1. Of or relating to the fifth member of a particular ordered set.

  2. Relating to or characterizing a polypeptide chain that is one of five types of heavy chains present in immunoglobins.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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epsilon in Technology
A macro language with high level features including strings and lists, developed by A.P. Ershov at Novosibirsk in 1967. EPSILON was used to implement ALGOL 68 on the M-220.
["Application of the Machine-Oriented Language Epsilon to Software Development", I.V. Pottosin et al, in Machine Oriented Higher Level Languages, W. van der Poel, N-H 1974, pp. 417-434].
[Jargon File]

1. The fifth letter of the Greek alphabet.
2. (From the Hungarian mathematician Paul Erdos) A very small, insignificant, or negligible quantity of something.
The use of epsilon is from the epsilon-delta method of proof in differential calculus.
The Free On-line Dictionary of Computing, © Denis Howe 2010
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