fogbow

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A faint white or yellowish arc-shaped light, similar to a rainbow, that sometimes appears in fog opposite the sun.

from The Century Dictionary.

• noun A faintish white arch seen in fog, similar to the rainbow, and due to the action of the same causes, the globules of water of the fog playing the same part as the raindrops.

from the GNU version of the Collaborative International Dictionary of English.

• noun A nebulous arch, or bow, of white or yellowish light sometimes seen in fog, etc.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun meteorology A white arc or circle, similar to a rainbow, which can appear in the sky in foggy conditions as sunlight passes through small airborne water droplets.