The Romans say that Echo was a nymph in love with Narcissus, but her love not being returned, she pined away till only her voice remained. We use the word to imply similarity of sentiment: as You echo my ideas; That is an echo to my opinion.
Sweet Echo, sweetest nymph, that liv'st unseen Within thy airy shell, By slow Meänder's margent green ... Canst thou not tell me of a gentle pair That likest thy Narcissus are?
Milton: Comus, 230, etc.
(Gr., eko; verb, ekeo, to sound.)