What does mu mean?
Mu most directly names the thirteenth letter of the Greek alphabet, whose lowercase symbol, μ, appears in mathematics, physics, and the international system of units. The letter’s shape inspired the SI prefix micro-, meaning one millionth, although the prefix ultimately comes from the Greek word mikros, meaning small. Scientists also use μ as the symbol for magnetic permeability and, in statistics, for the arithmetic mean of a set of values. A separate sense comes from Japanese Zen philosophy, where mu refers to undifferentiated emptiness or the absence of an independently existing essence. In this philosophical use, mu is more specific than the broad Buddhist idea of emptiness and is often discussed in relation to non-dual thought. The word is therefore both a familiar letter name and a specialist philosophical term, with its pronunciation and cultural associations shifting according to context.
nounThe thirteenth letter of the Greek alphabet, represented by the symbol μ or Μ. By extension, mu is a Japanese philosophical term meaning undifferentiated nothingness or emptiness.
- The thirteenth letter of the Greek alphabet, written μ in its lowercase form and Μ in its uppercase form.
- A symbol used in physics and mathematics, including for magnetic permeability and the mean value of a set of values.
- In Zen philosophy, the Japanese term for emptiness or the absence of an independently existing essence.
- An SI prefix symbol representing one millionth, written in front of a unit name and symbol.
"The Greek letter mu is used in physics to denote magnetic permeability and the prefix micro-."
"The scientist recorded the magnetic permeability, μ, for each sample."
"In Zen thought, mu suggests that an object has no fixed, independent essence apart from its changing relations."
The regular plural is used when referring to the letter as an item, as in a list of the Greek alphabet.
"The two mus appeared on opposite sides of the equation."
One Greek letter became a scientific workhorse: physicists adopted mu as the symbol for magnetic permeability and as the visual inspiration for the metric prefix micro-.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does mu come from?
The name mu comes from the Greek letter μ, which historically developed from the earlier Phoenician alphabet through the Greek adoption and stylization of its sign for mem. Greek forms of the letter varied in shape over time before settling into the familiar lowercase μ and uppercase Μ. The separate philosophical use entered English from Japanese 無, read mu, a Sino-Japanese character meaning absence or nothingness.
Related word forms
How mu is actually used
As the name of a Greek letter, mu is written as mu in running text and as Μ when capitalized. As a Zen term, it is usually italicized or kept in its original Japanese form 無 and is distinct from the Buddhist concept of emptiness in general. In scientific notation, the symbol μ may indicate a micro- prefix rather than the Greek letter as a word.
Easily confused with mu
Mu can name a Greek letter or the Zen concept of emptiness, whereas mew means to cry like a cat.