Definition of "proportional"

proportional

adjective
comparative more proportional, superlative most proportional
1. (mathematics) At a constant ratio (to). Two magnitudes (numbers) are said to be proportional if the second varies in a direct relation arithmetically to the first. Symbol: ∝.
  Quotations
  For example, according to the gas laws, pressure is directly proportional to temperature: the quotient derived from pressure (numerator) and temperature (denominator) will be constant; however, pressure is inversely proportional to volume, meaning that the product between volume and pressure will be constant.
  2012, David Ben-Chaim, Ratio and Proportion, page 34
2. (chiefly US) In proportion (to), proportionate.
  Quotations
  This ensures consistency across your website design so that you don't end up with elements that are not adequately proportional with each other.
  2014, Aravind Shenoy, Learning Bootstrap
3. Of a typeface, having characters with natural (non-uniform) width (in contrast to monospace typefaces).
  Quotations
  A font is proportional if all characters in the font have different widths due to their various sizes.
  2013, Eric A. Meyer, CSS Fonts: Web Typography Possibilities, page 2
noun
plural proportionals
1. (mathematics, geometry, archaic) A proportion.
  Quotations
  It is almost superfluous to remark that the numbers attached to the elements of compounds are those of the proportionals in which they combine […]
  1828, William Thomas Brande, Tables in Illustration of the Theory of Definite Proportionals, page xiii