Merriam-Webster's Collegiate® Dictionary, 11th Edition
VOLATILE
I. adjective
Etymology: French, from Latin volatilis, from volare to fly
Date: 1605
readily vaporizable at a relatively low temperature, flying or having the power to fly,
3. lighthearted , lively , easily aroused , tending to erupt into violence ; explosive ,
4. unable to hold the attention fixed because of an inherent lightness or fickleness of disposition, characterized by or subject to rapid or unexpected change , difficult to capture or hold permanently ; evanescent , transitory , volatileness noun volatility noun
II. noun
Date: 1686
a volatile substance