The Greek letters a reader meets in formulae without ever being told their names. Grouped because they share a problem rather than a meaning: none of them means anything on its own, and what each denotes is fixed by the field it appears in. Lambda is a wavelength in optics and an eigenvalue in linear algebra; alpha is a particle in physics and a significance level in statistics. Two of them are also the source of symbols the catalogue holds separately — the ohm sign is a capital omega, the summation sign a capital sigma — and telling those apart is a real question with a real answer.
The first Greek letter, used across science for angles, rates and particles.
The second Greek letter, used for beta particles, coefficients and angles.
The third Greek letter, used for gamma rays, functions and display response.
The fourth Greek letter, meaning change or difference in almost every field.
The fifth Greek letter, conventionally a very small positive quantity.
The eighth Greek letter, the default name for an angle.
The eleventh Greek letter, used for wavelength, eigenvalues and anonymous functions.
The twelfth Greek letter, and the SI prefix for one millionth.
The eighteenth Greek letter, used for standard deviation and stress.
The seventeenth Greek letter, used for density and resistivity.
The twenty-first Greek letter, used for the golden ratio and magnetic flux.
The last Greek letter, used for angular velocity — and the source of the ohm sign.
The Greek letter used for the ratio of a circle's circumference to its diameter.