The DICT Development Group

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

  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.?
  

  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)
  

  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)