- A part considered in relation to the whole.
- A relationship between things or parts of things with respect to comparative magnitude, quantity, or degree: the proper proportion between oil and vinegar in the dressing.
- A relationship between quantities such that if one varies then another varies in a manner dependent on the first: "We do not always find visible happiness in proportion to visible virtue" (Samuel Johnson).
- Agreeable or harmonious relation of parts within a whole; balance or symmetry.
- Dimensions; size. Often used in the plural.
- Mathematics A statement of equality between two ratios. Four quantities, a, b, c, d, are said to be in proportion if a/b = c/d.