adjective

- having due proportion; corresponding.
- being in or characterized by proportion.
- of, relating to, or based on proportion; relative.
- Mathematics.
- (of two quantities) having the same or a constant ratio or relation: The quantities y and x are proportional if y/x = k, where k is the constant of proportionality.
- (of a first quantity with respect to a second quantity) a constant multiple of: The quantity y is proportional to x if y = kx, where k is the constant of proportionality.

adjective

- of, involving, or being in proportion
- maths having or related by a constant ratio

noun

- maths an unknown term in a proportionin a/b = c/x, x is the fourth proportional

adj.late 14c. (implied in proportionally), from Late Latin proportionalis “pertaining to proportions,” from proportio (see proportion). Related: Proportionally.