Meaning : The property of relative size or extent (whether large or small).
Example :
They tried to predict the magnitude of the explosion.
About the magnitude of a small pea.
Meaning : A number assigned to the ratio of two quantities. Two quantities are of the same order of magnitude if one is less than 10 times as large as the other. The number of magnitudes that the quantities differ is specified to within a power of 10.
Synonyms : order of magnitude
Meaning : Relative importance.
Example :
A problem of the first magnitude.