[ep-suh-lon, -luh n or, esp. British, ep-sahy-luh n]


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)
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for epsilon

Historical Examples of epsilon

  • I dreamed they all committed suicide because Epsilon was too good for them.


    James Causey

  • And goeth from Epsilon down to Mu: the reference is to some numbering on the parchment.

  • A pilot comes back from Epsilon Eridani, for example, and insists on giving everybody left-handed salutes.

    Next Door, Next World

    Robert Donald Locke

  • 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

  • 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

British Dictionary definitions for epsilon



the fifth letter of the Greek alphabet (Ε, ε), a short vowel, transliterated as e

Word Origin for epsilon

Greek e psilon, literally: simple e



(foll by the genitive case of a specified constellation) the fifth brightest star in a constellationEpsilon 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

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

epsilon in Medicine


[ĕpsə-lŏn′, -lən]


The fifth letter of the Greek alphabet.
The fifth in a series.


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