1. the relative magnitudes of two quantities (usually expressed as a quotient)
2. the relation between things (or parts of things) with respect to their comparative quantity, magnitude, or degree
an inordinate proportion of the book is given over to quotations|a dry martini has a large proportion of gin
3. 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.