<unk> of an element or compound is a transition from the solid to gas phase with no intermediate liquid stage.<unk> is a phase transition that occurs at temperatures and pressures below the triple point (see phase diagram).
At normal pressures, most chemical compounds and elements possess three different states at different temperatures.  In these cases the transition from the solid to the gaseous state requires an intermediate liquid state.  However, for some elements or substances at some pressures the material may pass directly from solid to the gaseous state. This can occur if the atmospheric pressure exerted on the substance is too low to stop the molecules from escaping from the solid state.
The opposite of<unk> is deposition. The formation of frost is an example of meteorological deposition.
Sublimation 
Splitting 
Induction 
Exaptation
Formication
Anise
Transactivation
Penetrance