why does macbeth refer to the dagger as 'fatal vision"?

In Act II scene I Macbeth has a vision whereby he sees a dagger floating in mid-air, which points towards the chamber of Duncan.

Is this a dagger which I see before me,

The handle toward my hand? Come, let me clutch thee.

I have thee not, and yet I see thee still.

Art thou not, fatal vision, sensible

To feeling as to sight? or art thou but

A dagger of the mind, a false creation,

Proceeding from the heat-oppressed brain?

I see thee yet, in form as palpable

As this which now I draw.

The dagger is a fatal vision as it foreshadows the death of Duncan at the hands of Macbeth that night, and also Duncan's two servants. The dagger is also a 'fatal vision' as it leads to the deaths of many others, including Macbeth himself.