dampen

verb

1. (transitive)To make damp or moist; to make moderately wet.
2. (intransitive)To become damp or moist.
3. (transitive)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.”

   “He was dreadfully familiar with everything, and talked about some places we were longing to see in a way that considerably dampened our enthusiasm.”

   “Pregnant women are 20 times as likely as other healthy young women to contract listeriosis, probably because in pregnancy the immune system is dampened to prevent rejection of the fetus.”

   “The firm said changes in consumer behaviour had also dampened demand for the powder.”

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