A word or phrase that repeats throughout the work, but each time it picks up new meaning or additional baggage, so that when it is used at a key point, it has a viseral effect on the reader. (Run for the Hankies). A good example is from the film Ghost, (many authorial techniques come from or lend themselves to cinematography), the word ditto is an echo, which by the time it's delivered at the climax point, packs a powerful emotional whallop. My favorite echo is from the 1940's tearjerker Imitation of Life (often called the tear-jerker of the century). There the echo is a phrase (I kid you not) I want my ducky. That unlikely bit of echoing send millions into post-theater trauma. I've used such words as clot and Wham! Bam! Boom! as echos and, my favorite, I am your Rachel in Turning Idolater.
Edward C. Patterson