wraith

Merriam-Webster's Word of the Day for March 29, 2011 is:

wraith • \RAYTH\  • noun
1 a : the exact likeness of a living person seen usually just before death as an apparition b : ghost, specter 2 : an insubstantial form or semblance : shadow 3 : a barely visible gaseous or vaporous column

Examples:
We paused on our morning hike to watch the wraiths of mist rising from the swamps beyond the low hills in front of us.

Esben and the Witch take their name from a spooky Danish fairy tale. We expect dark gothic vibes and a singer who sounds like an eerie female wraith. We get both in Violet Cries. But this ambitious debut album also delivers much more. -- From a review by Ludovic Hunter-Tilney in the Financial Times, January 29, 2011

Did you know?
If you see your own double, you're in trouble, at least if you believe old superstitions. The belief that a ghostly twin's appearance portends death is one common to many cultures. In German folklore, such an apparition was called a Doppelgänger (literally, double goers); in Scottish lore, they were wraiths. The exact origin of the word wraith is misty, however. Etymologists can only trace it back to its first use in an English text in a 1513 translation of Virgil’s Aeneid by Gavin Douglas (the Scotsman used “wraith” to name apparitions of both the dead and the living). In current English, wraith has taken on additional, less spooky, meanings as well; it now often suggests a shadowy -- but not necessarily scary -- lack of substance.