epsilon; Ε, ε +

(Greek: the fifth letter of the Greek alphabet; Ε, ε)

In astronomy, the name for Uranus' most distant and most visible ring.
1. The fifth letter and second vowel of the Greek alphabet (Ε, ε) equivalent to the English short e.
2. As a numeral, it refers to to 5; relating to the fifth member of a particular ordered set.
3. In mathematics, an arbitrarily small quantity, used to indicate that a given quantity is small, or close to zero.
epsilon toxin
A bacterial toxin produced by clostridium perfringens or anaerobic Gram-positive rod bacterium that produces epsilon toxin.

It causes intense abdominal cramps and diarrhea that begins 8-22 hours after consumption of foods containing large numbers of these bacteria.

epsilon-aminocaproic acid
A synthetic substance used to correct an overdose of certain fibrinolytic agents (causing the dissolution of fibrin or blood-clotting by enzymatic action or a chemical that is produced by living cells which is a biochemical catalyst).

It is also useful in treating excessive bleeding due to increased fibrinolytic activity in the blood.

Referring to a method or proof in calculus involving arbitrarily small numbers.
epsilon-neighborhoods, epsilon neighborhood
1. The set of all points whose distance from a given point is less than some specified number epsilon.
2. The term epsilon neighborhood (or ε-neighborhood) is often used to emphasize that ε is arbitrarily small.

You can see all of the letters of the Greek Alphabet on this page.