WeatherTalk: Rime and hoarfrost are different, but about the same
Rime forms from water droplets while hoarfrost forms from water vapor
The correct scientific term for the feathery ice crystals which have coated our landscape many times recently is "rime." Tiny droplets of water in fog adhere to rough surfaces which encourage the supercooled (subfreezing) water to instantly freeze into delicate crystals. Technically, frost is formed from water vapor in the air, whereas rime comes from liquid droplets. The two look approximately the same; the difference is primarily one of formation.
When freezing fog occurs in the presence of a breeze, the rime tends to form on the windward side of objects, leaving the lee sides ice-free. "Rime" is an ancient, Proto-Indo-European word referring to a collection of things. The term "hoarfrost" is an Old English word and is thought to be a reference to an old man's beard.