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late 14c., from Anglo-French vapour, from Latin vaporem (nominative vapor) "exhalation, steam, heat," of unknown origin. Vapors "fit of fainting, hysteria, etc." is 1660s, from medieval notion of "exhalations" from the stomach or other organs affecting the brain.
vapor va·por (vā'pər)
Barely visible or cloudy diffused matter, such as mist, fumes, or smoke, suspended in the air.
The state of a substance that exists below its critical temperature and that may be liquefied by application of sufficient pressure.
The gaseous state of a substance that is liquid or solid under ordinary conditions.
The vaporized form of a medicinal preparation to be administered by inhalation.
A mixture of a vapor and air, as an explosive mixture of gasoline and air burned in an internal-combustion engine.
vapors Exhalations within an organ, especially the stomach, supposed to affect the mental or physical condition. No longer in technical use.
vapors A nervous disorder such as depression or hysteria. No longer in technical use.
Our Living Language : The words vapor and steam usually call to mind a fine mist, such as that in the jet of water droplets near the spout of a boiling teakettle or in a bathroom after a shower. Vapor and steam, however, refer to the gaseous state of a substance. The fumes that arise when volatile substances such as alcohol and gasoline evaporate, for example, are vapors. The visible stream of water droplets rushing out of a teakettle spout is not steam. As the gaseous state of water heated past its boiling point, steam is invisible. Usually, there is a space of an inch or two between the spout and the beginning of the stream of droplets. This space contains steam. The steam loses its heat to the surrounding air, then falls below the boiling point and condenses in the air as water droplets. All liquids and solids give off vapors consisting of molecules that have evaporated from the substance. In a closed system, the vapor pressure of these molecules reaches an equilibrium at which the substance evaporates from the liquid (or solid) and recondenses on it in equal amounts.