noun (n)

• the relative magnitudes of two quantities (usually expressed as a quotient)(noun.linkdef)

  source: wordnet30
• the relation between things (or parts of things) with respect to their comparative quantity, magnitude, or degree(noun.linkdef)

  Synonym:
  proportion
  

  source: wordnet30
• The relation which one quantity or magnitude has to another of the same kind. It is expressed by the quotient of the division of the first by the second; thus, the ratio of 3 to 6 is expressed by &frac36; or ½; of a to b by a/b; or (less commonly) the second term is made the dividend; as, a:b = b/a.(noun)

  source: webster1913