The Collaborative International Dictionary of English v.0.48:

Damp \Damp\ (d[a^]mp), n. [Akin to LG., D., & Dan. damp vapor,
   steam, fog, G. dampf, Icel. dampi, Sw. damb dust, and to MNG.
   dimpfen to smoke, imp. dampf.]
   1. Moisture; humidity; fog; fogginess; vapor.
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            Night . . . with black air
            Accompanied, with damps and dreadful gloom.
                                                  --Milton.
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   2. Dejection; depression; cloud of the mind.
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            Even now, while thus I stand blest in thy presence,
            A secret damp of grief comes o'er my soul.
                                                  --Addison.
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            It must have thrown a damp over your autumn
            excursion.                            --J. D.
                                                  Forbes.
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   3. (Mining) A gaseous product, formed in coal mines, old
      wells, pints, etc.
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   Choke damp, a damp consisting principally of carbonic acid
      gas; -- so called from its extinguishing flame and animal
      life. See Carbonic acid, under Carbonic.

   Damp sheet, a curtain in a mine gallery to direct air
      currents and prevent accumulation of gas.

   Fire damp, a damp consisting chiefly of light carbureted
      hydrogen; -- so called from its tendence to explode when
      mixed with atmospheric air and brought into contact with
      flame.
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