1. Also called undulatory theory. Physics.the theory that light is transmitted as a wave, similar to oscillations in magnetic and electric fields. Cf. corpuscular theory.
2. Historical Ling.a theory that accounts for shared features among languages or dialects by identifying these features as innovations that spread from their points of origin to the speech of contiguous areas. Cf. family-tree theory.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.