What literary device does the word "nevermore" represent in The Raven?

The repetition of the
word "Nevermore" is a refrain, coming in the final line of each stanza where it
appears. First, the speaker asks for the raven's name, suggesting that it comes from the
Underworld, and it responds, "Nevermore." Next, the speaker assumes that this is the
bird's name. Third, he starts to think that the word is the one word that the bird learned from
its former owner. Fourth, he pulls up a chair to consider the raven and what it might mean by
"croaking 'Nevermore.'" The fifth repetition of the word comes when the narrator
considers that his dead lover will never sit against the cushion of his chair ever again. Next,
the raven speaks the word again when the narrator decides that, perhaps, the bird was sent to
distract him from and help him forget his grief over . This implies that he was not sent by God,
as the narrator wonders. Seventh, he asks if there is "balm in Gilead," ostensibly
some kind of cure for his grief (as a balm in Gilead means a cure of some
kind), and the raven answers, "Nevermore." Next, the speaker orders the bird to leave
him forever, and the raven refuses. Finally, the speaker says that the shadow of the bird will
be "lifted" from his floor "nevermore!"