What does "buzzkill" mean?

Something that or someone who spoils an otherwise enjoyable event.

What is a synonym for "buzzkill"?

Common synonyms include: killjoy, spoilsport, wet blanket, dampener, downer, downers.

/ˈbʌzkɪl/ noun, slang

noun, slang ·Moderate ·College level

Noun

1
Something that or someone who spoils an otherwise enjoyable event. idiomatic, slang
2
A person who attends a social event and occupies their time with unsociable activities. idiomatic, slang

From buzz (“feeling of energy or excitement”) + kill.