Dampen

Verb

1. To make damp or moist; to make moderately wet.
2. To become damp or moist.
3. To lessen; to dull; to make less intense (said of emotions and non-physical things).

   "We won't let the bad news dampen our spirits."

4. To suppress vibrations (mechanical) or oscillations (electrical) by converting energy to heat (or some other form of energy).
5. To become damped or deadened.