To discourage or dishearten; also, to decrease the intensity of something: Insects put a damper on my plans to move to Maine
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with 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.