A "poetic device" is a use of words to create a certain kind of effect upon the reader. Poets may choose certain words to give a specific impact through their combined sounds, through the meanings they convey, or in other ways. In "The Raven," Poe uses many poetic devices.
Alliteration is the use of the same initial sound, usually a consonant, in several words. Poe uses this device when he writes phrases such as "weak and weary...quaint and curious...nodded, nearly napping."
Ambiguity refers to a situation in which a text may be understood in more than one way. The raven's cry of "Nevermore" could be telling the given name of the raven, could be telling the speaker that he will never see his beloved Lenore again, could be a prediction that the speaker will never again be free from the haunting memories and depths of grief filling his being.
The repetition of "Quoth the Raven, 'Nevermore'" also serves as a refrain in the poem - a recurring rhythm and combination of sounds at the end of many of the stanzas that helps to reinforce the meter and rhyme of the poem.
Rhyme is used throughout the poem, at the end of lines and within the lines themselves. The use of rhymes drives the rhythm and supports the build-up of tension and tightly-woven storytelling as the poem progresses.