VA'POR, n. [L. vapor.]

1. In a general sense, an invisible elastic fluid, rendered aeriform by heat, and capable of being condensed, or brought back to the liquid or solid state, by cold. The vapor of water is distinguished by the name of steam, – which see.
2. A visible fluid floating in the atmosphere. All substances which impair the transparency of the atmosphere, as smoke, fog, &c., are in common language called vapors, though the term vapor is technically applied only to an invisible and condensible substance, as in No. 1; fog, &c. being vapor condensed, or water in a minute state of division. Vapor rising into the higher regions of the atmosphere, and condensed in large volumes, forms clouds. – D. Olmsted.
3. Substances resembling smoke, which sometimes fill the atmosphere, particularly in America during the autumn.
4. Wind; flatulence. – Bacon.
5. Mental fume; vain imagination; unreal fancy. – Hammond.
6. Vapors, a disease of nervous debility, in which a variety of strange images float in the brain, or appear as if visible. Hence hypochondriacal affections and spleen are called vapors.
7. Something unsubstantial, fleeting, or transitory. For what is your life? It is even a vapor, that appeareth for a little time, and then vanisheth away. James iv.

1. To pass off in fumes or a moist floating substance; to steam; to be exhaled; to evaporate. [In this sense, evaporate is generally used.]
2. To emit fumes. Running water vapors not so much as standing water. [Little used.] – Bacon.
3. To bully; to boast or vaunt with a vain, ostentatious display of worth; to brag. [This is the most usual signification of the word.] And what in real value's wanting, / Supply with vaporing and ranting. – Hudibras.

To emit, cast off, or scatter in fumes or steam; as, to vapor away a heated fluid. Another sighing vapors forth his soul. – B. Jonson.

1. 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.

2. To pass off in fumes, or as a moist, floating substance, whether visible or invisible, to steam] to be exhaled; to evaporate.
3. To send off in vapor, or as if in vapor; as, to vapor away a heated fluid.
   
   
   [Written also vapour.]

   He'd laugh to see one throw his heart away,
   Another, sighing, vapor forth his soul. B. Jonson.

4. In a loose and popular sense, any visible diffused substance floating in the atmosphere and impairing its transparency, as smoke, fog, etc.
   
   

   The vapour which that fro the earth glood [glided]. Chaucer.

   Fire and hail; snow and vapors; stormy wind fulfilling his word. Ps. cxlviii. 8.

5. To emit vapor or fumes.
   
   
   [R.]

   Running waters vapor not so much as standing waters. Bacon.

6. Wind; flatulence.
   
   
   [Obs.] Bacon.
7. To talk idly; to boast or vaunt; to brag.
   
   

   Poets used to vapor much after this manner. Milton.

   We vapor and say, By this time Matthews has beaten them. Walpole.

8. Something unsubstantial, fleeting, or transitory; unreal fancy; vain imagination; idle talk; boasting.
   
   

   For what is your life? It is even a vapor, that appeareth for a little time, and then vanisheth away. James iv. 14.

9. An old name for hypochondria, or melancholy; the blues.
   
   
   "A fit of vapors." Pope.
10. A medicinal agent designed for administration in the form of inhaled vapor.
    
    
    Brit. Pharm.

    Vapor bath. (a) A bath in vapor; the application of vapor to the body, or part of it, in a close place; also, the place itself. (b) (Chem.) A small metallic drying oven, usually of copper, for drying and heating filter papers, precipitates, etc.; -- called also air bath. A modified form is provided with a jacket in the outside partition for holding water, or other volatile liquid, by which the temperature may be limited exactly to the required degree. -- Vapor burner, a burner for burning a vaporized hydrocarbon. -- Vapor density (Chem.), the relative weight of gases and vapors as compared with some specific standard, usually hydrogen, but sometimes air. The vapor density of gases and vaporizable substances as compared with hydrogen, when multiplied by two, or when compared with air and multiplied by 28.8, gives the molecular weight. -- Vapor engine, an engine worked by the expansive force of a vapor, esp. a vapor other than steam.