An echo is a repetition or imitation of sound. When sound waves hit a hard surface they might reflect, making the sound bounce and repeat. If you agree with someone, you might echo his or her statement.
Poet Don Marquis said, “Writing a book of poetry is like dropping a rose petal down the Grand Canyon and waiting for the echo.” The word echo came from the Greek word for "sound." In Greek mythology, Echo was a nymph who could only repeat the last words of others. You were frightened when you thought someone was following you, until you realized you were only hearing the echo of your own footsteps.