Source : Webster's Revised Unabridged Dictionary (1913)

Dampen \Damp"en\, v. t. [imp. & p. p. {Dampened}; p. pr. & vb.
   n. {Dampening}.]
   1. To make damp or moist; to make slightly wet.

   2. To depress; to check; to make dull; to lessen.

            In a way that considerably dampened our enthusiasm.
                                                  --The Century.

Source : WordNet®

dampening
     n : the act of making something slightly wet [syn: {moistening}]