The Collaborative International Dictionary of English v.0.48:

Dampen \Damp"en\ (d[a^]mp"'n), v. t. [imp. & p. p. dampened
   (d[a^]mp"'nd); p. pr. & vb. n. dampening.]
   1. To make damp or moist; to make slightly wet.
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   2. To depress; to check; to make dull; to lessen.
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            In a way that considerably dampened our enthusiasm.
                                                  --The Century.
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