sublimation

A change of state of matter, directly from solid phase to gaseous phase without passing through the liquid phase. The reverse process (from vapor to solid) is called reverse sublimation, although in Meteorology it is common to refer to both processes - the direct and the reverse - as sublimation. The formation of hoarfrost or the growth of the ice crystals forming snow are the result of the sublimation of water vapor present in the air.