Definition of magnitude noun from the Oxford Advanced American Dictionary

magnitude

noun
/ˈmæɡnəˌtud/
 
magnitude (of something)
 
1 [uncountable] (formal) the great size or importance of something; the degree to which something is large or importantWe did not realize the magnitude of the problem.a discovery of the first magnitude2 [countable, uncountable] (astronomy) the degree to which a star is brightThe star varies in brightness by about three magnitudes.3 [countable, uncountable] (geology) the size of an earthquakeThe quake reached a magnitude of 7.1 on the Richter scale.