Real Dictionary

echo
countable noun: An echo is a sound which is caused by a noise being reflected off a surface such as a wall.
verb: If a sound echoes, it is reflected off a surface and can be heard again after the original sound has stopped.

echo in American English
the repetition of a sound by reflection of sound waves from a surface
to repeat (another's words, ideas, etc.)
to resound with an echo; reverberate
noun: a repetition of sound produced by the reflection of sound waves from a wall, mountain, or other obstructing surface

Echo in British English 1
noun: either of two US passive communications satellites, the first of which was launched in 1960

Echo in British English 2
noun: a nymph who, spurned by Narcissus, pined away until only her voice remained

Echo in British English 3
noun: code word for the letter e