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 substance for use in industrial, military, or medical processes. A mixture of a vapor and air, as the explosive gasoline-air mixture burned in an internal-combustion engine. Archaic Something insubstantial, worthless, or fleeting. Archaic A fantastic or foolish idea. Archaic Exhalations within a bodily organ, especially the stomach, supposed to affect the mental or physical condition. Used with the. Archaic A nervous disorder such as depression or hysteria. Used with the. To vaporize. To give off vapor. To evaporate. To engage in idle, boastful talk.