Definition of "magnitude"

magnitude

/ˈmæɡnɪtjuːd/

noun
countable and uncountable, plural magnitudes
1. (uncountable, countable) The absolute or relative size, extent or importance of something.
  Quotations
  And on a programme of works of this magnitude, passengers will need to be mindful of the age-old maxim of 'no gain without pain'.
  2020 September 23, Paul Stephen, “East Coast upgrade: changes to schedule... but on schedule”, in Rail, page 31
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.
    Quotations
    Observations in the infrared domain allow one to penetrate the ~25-30 magnitudes of extinction present at visible wavelengths.
    2005, Andreas Eckart et al., The Black Hole at the Center of the Milky Way‎, page 71
6. (seismology) A measure of the energy released by an earthquake (e.g. on the Richter scale).