Definition:

1.noun[C]
    A sound that is heard after it has been reflected off a surface such as a wall or a cliff
 

(from Cambridge Dictionary)
2.noun[C]
    A detail that is similar to and makes you remember something else

(from Cambridge Dictionary)

Orgin:

In Greek mythology, Echo was an Oread who resided on Mount Cithaeron. Zeus loved consorting with beautiful nymphs and often visited them on Earth. Eventually, Zeus's wife, Hera, became suspicious, and came from Mt. Olympus in an attempt to catch Zeus with the nymphs. Echo, by trying to protect Zeus, endured Hera's wrath, and Hera made her only able to speak the last few words spoken to her. So when Echo met Narcissus and fell in love with him, she was unable to tell him how she felt and was forced to watch him as he fell in love with himself.

Example Sentence:

Sam shouted to the cliff and the echo surround in the valley in a second.