Specter (noun)

1. A ghost or phantom appearing in a visible form, especially one believed to be the spirit of a dead person.
2. An apparition, or a phantom.
3. A phantom, or a ghostly appearance.

Origin:

Late middle english: from old french spectre, from latin spectrum 'apparition, image', from specere 'to look'.

Examples:

1. The old castle was said to be haunted by the specter of a former owner.
2. The specter of death loomed over the battlefield.
3. The young girl screamed when she saw the specter in her room.
4. The specter was seen only in the darkness, never in the light.
5. The specter was a warning of things to come, a harbinger of doom.