Dictionary
Dop'pler effect"
Pronunciation: (dop'lur), [key] Physics.
(often l.c.) the shift in frequency
(Dop'pler shift") of acoustic or electromagnetic radiation emitted by a source moving relative to an observer as perceived by the observer: the shift is to higher frequencies when the source approaches and to lower frequencies when it recedes.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.