n. Dew-drops which have undergone deposition and frozen into ice crystals to form a white deposit on an exposed surface, when the air is cold and moist.
the GNU version of the Collaborative International Dictionary of English
n. The white particles formed by the congelation of dew; white frost.
The Century Dictionary and Cyclopedia
n. White frost. See hoar, a., and frost.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. ice crystals forming a white deposit (especially on objects outside)
Word Usage
"I did have to look it up, not sure myself, but the explanation was simple really, frozen dew, but the word hoarfrost sounds much more mystical."