volatile

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Evaporating readily at normal temperatures and pressures.
• adjective Capable of being readily vaporized.
• adjective Tending to vary often or widely, as in price.
• adjective Inconstant; fickle.
• adjective Lighthearted; flighty.
• adjective Ephemeral; fleeting.
• adjective Tending to violence; explosive.
• adjective Flying or capable of flying; volant.
• adjective Computers Of or relating to memory whose data is erased when the memory's power is interrupted.

from The Century Dictionary.

• Having the power of being readily converted into gas or vapor. Sometimes applied, in chemistry, to those constituents, or that portion, of a substance which is driven off by heating at a specified temperature.
• Flying, or able to fly; having the power of flight; volant; volitant.
• Having the quality of taking flight or passing off by spontaneous evaporation; evaporating rapidly; becoming diffused more or less freely in the atmosphere.
• Lively; brisk; gay; full of spirit; airy; hence, fickle; apt to change: as, a volatile disposition.
• Transient; not permanent; not lasting.
• noun A winged creature, as a bird or butterfly.
• noun Wild fowl collectively.

from the GNU version of the Collaborative International Dictionary of English.

• adjective obsolete Passing through the air on wings, or by the buoyant force of the atmosphere; flying; having the power to fly.
• adjective Capable of wasting away, or of easily passing into the aëriform state; subject to evaporation.
• adjective Fig.: Light-hearted; easily affected by circumstances; airy; lively; hence, changeable; fickle.
• adjective (Old Chem.) See under Alkali.
• adjective a liniment composed of sweet oil and ammonia, so called from the readiness with which the latter evaporates.
• adjective (Chem.) See Essential oils, under Essential.
• noun obsolete A winged animal; wild fowl; game.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective physics evaporating or vaporizing readily under normal conditions.
• adjective of a substance, informal explosive.
• adjective of a price, etc. variable or erratic.
• adjective of a person quick to become angry or violent.
• adjective fickle.
• adjective temporary or ephemeral.
• adjective of a situation potentially violent.
• adjective computing, of a variable having its associated memory immediately updated with any changes in value.
• adjective computing whose content is lost when the computer is powered down

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective tending to vary often or widely
• adjective liable to lead to sudden change or violence
• adjective marked by erratic changeableness in affections or attachments
• noun a volatile substance; a substance that changes readily from solid or liquid to a vapor
• adjective evaporating readily at normal temperatures and pressures