ˈ ̷ ̷ˌ ̷ ̷ noun
Etymology: kill (I) + joy
: one that inspires gloom or counteracts joy or high spirits : one that tends to pessimism or a depressing solemnness especially among people that are happy or optimistic : one that dispirits
professional killjoys whose chief fear it is that people … might get some fun out of life — T.P.Whitney