"ech·o
n. pl. ech·oes

Repetition of a sound by reflection of sound waves from a surface.
The sound produced in this manner.
A repetition or an imitation: a fashion that is an echo of an earlier style.
A remnant or vestige: found echoes of past civilizations while examining artifacts in the Middle East.
One who imitates another, as in opinions, speech, or dress.
A sympathetic response: Their demand for justice found an echo in communities across the nation.
A consequence or repercussion: Her resignation had echoes throughout the department.
Repetition of certain sounds or syllables in poetry, as in echo verse.
Music. Soft repetition of a note or phrase.
Electronics. A reflected wave received by a radio or radar." source

" 'a duck's quack doesn't echo, and no one knows why'
actually it does echo, but the sound wave for both the initial quack and the secondary sound caused by the echo are so close they can not be sorted out without the use of sophisticated audio equipment. (Thanks to Mythbusters on the Discovery Channel for wasted production time on this one!)" source


"University of Maryland scientists say echo-locating bats use a strategy to track and catch insects that's similar to a guided missile's tracking system." source


"The largest generation of young people since the '60s is beginning to come of age. They're called 'echo boomers' because they're the genetic offspring and demographic echo of their parents, the baby boomers.

Born between 1982 and 1995, there are nearly 80 million of them, and they're already having a huge impact on entire segments of the economy."source


"Filtering out useless information can help people increase their capacity to remember what is really important, researchers said on Wednesday." source