Old English forst, frost "a freezing, becoming frozen, extreme cold," from Proto-Germanic *frusta- (cf. Old Saxon, Old Frisian, Old High German frost, Middle Dutch and Dutch vorst), related to freosan "to freeze," from PIE *preus- "to freeze; burn" (see freeze (v.)). Both forms of the word were common in English till late 15c.; the triumph of frost may be due to its similarity to the forms in other Germanic languages.
A deposit of minute ice crystals formed when water vapor condenses at a temperature below freezing.
A deposit of tiny, white ice crystals on a surface. Frost forms through sublimation, when water vapor in the air condenses at a temperature below freezing. It gets its white color from tiny air bubbles trapped in the ice crystals. See more at dew point.