proportional (adj.)

late 14c. proporcional (implied in proporcionalli), "having a particular correspondence, according to or having a due proportion," from Old French proporcionel and directly from Late Latin proportionalis "pertaining to proportions," from proportio "comparative relation, analogy" (see proportion (n.)). The phrase proportional representation in the political sense for representation based on numerical proportion (rather than regional division) is attested by 1821. Related: Proportionally.

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Definitions of proportional from WordNet
proportional (adj.)
properly related in size or degree or other measurable characteristics; usually followed by `to';
the punishment ought to be proportional to the crime
Synonyms: relative
proportional (adj.)
having a constant ratio;
proportional (n.)
one of the quantities in a mathematical proportion;