Etymology: Middle English rim, from Old English hrIm; akin to Old Norse hrIm frost
1 : FROST 1b
2 : an accumulation of granular ice tufts on the windward sides of exposed objects that is formed from supercooled fog or cloud and built out directly against the wind
According to Wikipedia, "Rime ice is a white ice that forms when the water droplets in fog freeze to the outer surfaces of objects. It is often seen on trees atop mountains and ridges in winter, when low-hanging clouds cause freezing fog. This fog freezes to the windward (wind-facing) side of tree branches, buildings, and any other solid object.
Rime ice is similar in appearance hoar frost but whereas rime ice is formed by vapour first condensing to liquid droplets (of fog, mist or cloud) and then attaching to surface, hoar frost is formed by direct deposition from water vapour to solid ice.
Rime ice and glaze ice are also the two types of ice that can form on the surfaces of an aircraft, if it flies though a cloud made of supercooled water liquid droplets.
Rime ice is formed also inside of freezers, and on objects taken out of freezers on humid days, hoar frost is formed on their surfaces in a while."