magnitude

The absolute or relative size, extent or importance of something.

An order of magnitude.

A number, assigned to something, such that it may be compared to others numerically

Of a vector, the norm, most commonly, the two-norm.

A logarithmic scale of brightness defined so that a difference of 5 magnitudes is a factor of 100.

A measure of the energy released by an earthquake (e.g. on the Richter scale).