To discourage or dishearten; also, to decrease the intensity of something: Insects put a damper on my plans to move to Maine
Idioms and Phrases with put a damper on
put a damper on
Discourage, dishearten, deter, as in Grandpa's death put a damper on our Christmas holidays. This idiom employs the noun damper in the sense of “something that damps or depresses the spirits,” a usage dating from the mid-1700s.