What does "horror" mean?

Horror: A shaking, shivering, or shuddering, as in the cold fit which precedes a fever; in old medical writings, a chill of less severity than a rigor, and more marked than an algor.

Additional senses

  1. 2.A painful emotion of fear, dread, and abhorrence; a shuddering with terror and detestation; the feeling inspired by something frightful and shocking. How could this, in the sight of heaven, without horrors of conscience be uttered Milton.
  2. 3.That which excites horror or dread, or is horrible; gloom; dreariness. Breathes a browner horror on the woods. Pope. The horrors, delirium tremens. [Colloq.]

Sources