Epsilon Symbol: Origins, Meaning and Uses

Like many letters of the Greek alphabet, the letter Epsilon has made its way into modern culture as a useful symbol. It is no surprise that the letters used by the Greeks, who had such a big influence on modern western society, would have left their mark in other ways.

Epsilon is an important symbol in mathematics, science, astrology, and many other fields. Linked with both the sound “e” and the number five, you will be surprised all the places you see this symbol popping up.

The Greek Alphabet

Epsilon is one of the 24 letters of the Ancient Greek alphabet, the original language of the New Testament of the Bible among other important works.

The fifth letter in the alphabet, it was used to represent a sound very similar to e in the modern English alphabet. As the Greeks also used letters to denote numbers, as the fifth letter of the alphabet, Epsilon also represented the digit 5.

An uppercase Epsilon looks like a modern uppercase E in the English alphabet, but the lowercase Epsilon looks more like a reversed 3. The Greeks actually borrowed the symbol from the Phoenician alphabet, where it is used to represent the letter He.

The Name

The Greeks did not actually call their Epsilon by this name, but either “ei”, which is a reproduction of the basic sound of the letter. It was only in the Middle Ages that European scholars decided to call the symbol Epsilon, in order to more clearly differentiate it from the name for the digraph sound “ai”.


Like many Greek letters, the Epsilon is commonly used as a mathematical symbol. Like most of the Greek letters (with notable exceptions such as Pi which has a specific meaning) it can be used to represent any variable. But it is often used to represent an arbitrarily small numbers, such as a remainder that is so miniscule that it can be taken for zero.

In this case the Epsilon is associated with the word “error”, the remaining fraction being an acceptable mathematical error.

Other Sciences

In computer science, Epsilon is used to represent an empty string or an empty word in programming code. An empty string is when the string length is zero. This should not be confused with a null string, which is when the string has no value.

In biology, Epsilon is used to refer to how efficient a plant is at completing the photosynthesis process.

In engineering, the Epsilon I used to represent increase in length divided by original length.


Epsilon has also made its way into Astrology. It is the name for the fifth brightest star in a constellation, as the fifth letter of the Greek alphabet. It is also the name for the most distant, and more clearly visible, or Uranus’ rings.

It is also used to denote the axial tilt of a planet by astronomers.


The letter Epsilon is much more than just a letter that students need to learn if they want to study the classics or read the New Testament in its original language. The Greeks had a huge influence on modern philosophy and science, so it is no surprise that this Greek letter has a home there.

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