Dampen v. t. : To make damp or moist; to make slightly wet.

Dampen v. t. : To depress; to check; to make dull; to lessen.

Dampen v. i. : To become damp; to deaden.

Example:
How can you Dampen the sound between interior walls after a house has been built ?

Taxonomy
damp, Merriam-Webster Online Dictionary, Dictionary, webster, dam, Word Games, Webster Online Dictionary with audio pronunciations, thesaurus, glossary, english, language, ESL, Search, Inflected, ened, transitive verb, vigor, heat.

Defination from the web:
dampen from the Merriam-Webster Online Dictionary with audio pronunciations, thesaurus, Word of the Day, and word games. ... to check or diminish the activity or vigor of : deaden <the heat dampened our spirits> 2 : to make damp <the shower barely dampened the ground> ...