Repetition is a rhetorical device that repeats a word, a phrase or a sentence several times in order to add emphasis, unity, power or an artistic effect to an idea. In the excerpt, the lines "O Captain! My Captain!”? But O heart! heart! heart!" are a great example of repetition, more specifically it is an Epimone, which it's a type of repetition of a phrase or question aiming to emphasize or to dwell on a point.
Repetition refers to writing the same word more than once within a short space of words in order to emphasize an idea, or make it more memorable. It can also be used for clarity or emotional effect. Repetition can be used both in poetry and in prose. As a rhetorical device, it includes words, phrases and sentences.
