frost
n. C / Un. a thin layer of ice that forms on surfaces like grass or windows when the air is very cold. It looks like white powder or tiny crystals.
n. a deposit of small white ice crystals formed on the ground or other surfaces when the temperature falls below freezing. It occurs when water vapour in the air undergoes deposition directly into ice.
The grass is white with frost this morning.
Farmers are worried that an early frost might kill the delicate orange blossoms before they can turn into fruit.
The windowpanes were etched with intricate patterns of frost, obscuring the view of the frozen garden beyond with a delicate, crystalline lattice.
Uncountable when referring to the weather phenomenon in general; countable when referring to a specific instance of freezing weather.