Volatile (adjective)

1. Likely to change suddenly and unpredictably, especially for the worse.
2. Evaporating readily at normal temperatures and pressures.
3. Unpredictable or unstable.

Origin:

From the latin word "volatilis" meaning "flying" or "light".

Examples:

1. The stock market is volatile and can change rapidly.
2. The weather in the mountains is volatile and can change quickly.
3. The volatile liquid evaporated quickly.
4. The volatile political situation in the country made it hard to plan for the future.
5. The volatile emotions of the teenager made it hard to communicate with him.