The Collaborative International Dictionary of English v.0.48:
Vapor \Va"por\, n. [OE. vapour, OF. vapour, vapor, vapeur, F.
vapeur, L. vapor; probably for cvapor, and akin to Gr. ?
smoke, ? to breathe forth, Lith. kvepti to breathe, smell,
Russ. kopote fine soot. Cf. Vapid.] [Written also
1. (Physics) Any substance in the gaseous, or aeriform,
state, the condition of which is ordinarily that of a
liquid or solid.
Note: 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
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. 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].
Fire and hail; snow and vapors; stormy wind
fulfilling his word. --Ps. cxlviii.
3. Wind; flatulence. [Obs.] --Bacon.
4. 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.
5. pl. An old name for hypochondria, or melancholy; the
blues. "A fit of vapors." --Pope.
6. (Pharm.) A medicinal agent designed for administration in
the form of inhaled vapor. --Brit. Pharm.
(a) A bath in vapor; the application of vapor to the body,
or part of it, in a close place; also, the place
(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
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.