Evolution, n.

The unfolding or opening of a curve, and making it describe an evolvent. The equable evolution of the periphery of a circle, or other curve, is such a gradual approach of the circumference to rectitude, as that its parts do all concur, and equally evolve or unbend; so that the same line becomes successively a less arc of a reciprocally greater circle, till at last they change into a straight line.