1630s, "to dull or deaden, make weak" (force, enthusiasm, ardor, etc.), from damp (adj.) + -en (1). Meaning "to moisten, make humid" is recorded from 1827. Related: Dampened; dampening.
Entries linking to dampen
damp adj.
1580s, "dazed," from damp (n.). Meaning "slightly wet" is from 1706. Related: Damply; dampness.
-en 1
word-forming element making verbs (such as darken, weaken) from adjectives or nouns, from Old English -nian, from Proto-Germanic *-inojan (also source of Old Norse -na), from PIE adjectival suffix *-no-. Most active in Middle English and early modern English, hence most verbs in -en are comparatively recent.
dampener n.
"one who or that which dampens," 1857, agent noun from dampen.