Pronunciation: (ep'su-lon", -lun or, esp. Brit., ep-sī'lun), [key]
1. the fifth letter of the Greek alphabet (E, ε).
2. the consonant sound represented by this letter.
3. Math.an arbitrarily small quantity, used to indicate that a given quantity is small, or close to zero.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.