What does Elizabeth mean when she says, “Oh, the noose, the noose is up!”?

When Elizabeth Proctor says, "Oh, the noose, the noose is up!" she says it in response to Mary Warren's admission that her name was "mentioned" in court.  Mary will not tell who began to accuse Elizabeth of sending "[her] spirit out to hurt" them, but Elizabeth guesses that it was Abigail Williams, the girl she dismissed seven months earlier for having an affair with John, Elizabeth's husband.  

What she means is that Abigail wants her dead because she wants to get Elizabeth out of the way so that she and John can be together.  It is upon Abigail's charges that so many are arrested and condemned, and so Elizabeth fears that she will be next.  She says next that "[Abigail] wants [her] dead," because Abigail "thinks to kill [her], then to take [her] place."  She feels that "There is a promise made in any bed," and that Abigail is acting on her faith in that promise: she thinks that John loves her and would be with her if not for his wife.