volatile

Short definition from Wiktionary

Adjective

1. 1
   Evaporating or vaporizing readily under normal conditions.
2. 2
   Explosive.
3. 3
   Variable or erratic.
4. 4
   Quick to become angry or violent.
5. 5
   Fickle.
6. 6
   Temporary or ephemeral.
7. 7
   Potentially violent.
8. 8
   Having its associated memory immediately updated with any changes in value.
9. 9
   Whose content is lost when the computer is powered down.
10. 10
    Passing through the air on wings, or by the buoyant force of the atmosphere; flying; having the power to fly.

Noun

1. 1
   A chemical or compound that changes into a gas easily.
2. 2
   A variable that is volatile, i.e. has its associated memory immediately updated with any change in value.