epsilon

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."