A Magnitude

1. (uncountable, countable) The absolute or relative size, extent or importance of something.
2. (countable) An order of magnitude.
3. (mathematics) A number, assigned to something, such that it may be compared to others numerically
4. (mathematics) Of a vector, the norm, most commonly, the two-norm.
5. (astronomy) A logarithmic scale of brightness defined so that a difference of 5 magnitudes is a factor of 100.
   1. (uncountable) The apparent brightness of a star, with lower magnitudes being brighter; apparent magnitude
   2. (countable) A ratio of intensity expressed as a logarithm.
6. (seismology) A measure of the energy released by an earthquake (e.g. on the Richter scale).