dampen

Short definition from Wiktionary

Verb

1. 1
   To make damp or moist; to make moderately wet.
2. 2
   To become damp or moist.
3. 3
   To lessen; to dull; to make less intense (said of emotions and non-physical things).
4. 4
   To suppress vibrations (mechanical) or oscillations (electrical) by converting energy to heat (or some other form of energy).
5. 5
   To become damped or deadened.