Vā'por1, n.
n. [Lat., Pr., Sp., & Pg. vapor, Fr. vapeur, It. vapore.] [Written also vapour.]
Sense 1. (Physics.) Any substance in the gaseous or aëriform state, the condition of which is ordinarily that of a liquid or solid.
☞ The term vapor is sometimes used in a more extended sense, as identical with gas; and the difference between the two is not so much one of kind as of degree, the latter being applied to all permanently elastic fluids except atmospheric air, the former to those elastic fluids which lose that condition at ordinary temperatures. The atmosphere contains more or less vapor of water, a portion of which, on a reduction of temperature, becomes condensed into liquid water in the form of rain or dew. The vapor of water produced by boiling, especially in its economic relations, is called steam.
Vapor is any substance in the gaseous condition at the maximum of density consistent with that condition. This is the strict and proper meaning of the word vapor. Nichol.
Sense 2. In a loose and popular sense, any visible diffused substance floating in the atmosphere and impairing its transparency, as smoke, fog, or the like.
Sense 3. Wind; flatulence. [Obs.] Bacon.
Sense 4. Something unsubstantial, fleeting, or transitory; unreal fancy; vain imagination.
For what is your life? It is even a vapor, that appeareth for a little time, and then vanisheth away. James iv. 14.
Sense 5. (pl.) A disease of nervous debility, in which a variety of strange images float in the brain, or appear as if visible; hence, hypochondriacal affections; depression of spirit; dejection; spleen;—a term formerly much used, but now seldom employed.