WordNet (r) 3.0 (2006):

epsilon
    n 1: the 5th letter of the Greek alphabet

The Jargon File (version 4.4.7, 29 Dec 2003):

epsilon


    [see delta]

    1. n. A small quantity of anything. ?The cost is epsilon.?

    2. adj. Very small, negligible; less than marginal. ?We can get this
    feature for epsilon cost.?

    3. within epsilon of: close enough to be indistinguishable for all
    practical purposes, even closer than being within delta of. ?That's not
    what I asked for, but it's within epsilon of what I wanted.? Alternatively,
    it may mean not close enough, but very little is required to get it there:
    ?My program is within epsilon of working.?


The Free On-line Dictionary of Computing (30 December 2018):

EPSILON

    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]

   (1995-05-10)


The Free On-line Dictionary of Computing (30 December 2018):

epsilon
within epsilon of

   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.

   (2001-07-06)