the apparent change of frequency of sound waves or light waves, varying
with the relative velocity
of the source and the observer: if the source and observer are drawing
closer together, the observed frequency is higher
than the emitted
Webster’s New World College Dictionary, 4th Edition. Copyright © 2010 by
Houghton Mifflin Harcourt. All rights reserved.
Word origin of 'Doppler effect'after C. Doppler (1803-53), Austrian mathematician and physicist