noun (n)

• the property of relative size or extent (whether large or small)(noun.attribute)

  Example:
  They tried to predict the magnitude of the explosion.
  About the magnitude of a small pea.
  

  source: wordnet30
• 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(noun.linkdef)

  Synonym:
  order of magnitude
  

  source: wordnet30
• relative importance(noun.attribute)

  Example:
  A problem of the first magnitude.
  

  Synonym:
  prominence
  

  source: wordnet30
• Extent of dimensions; size; -- applied to things that have length, breadth, and thickness.(noun)

  source: webster1913