1
general::
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.
American Heritage Idioms
2
general::
Phrase(s): put a damper on something
Fig. to have a dulling or numbing influence on something. • The bad news really put a damper on everything. • The rainy weather put a damper on our picnic.
McGrawhill's American Idioms And Phrasal Verbs