IPA: /ˈθrɛtənər/
KK: /ˈθrɛtənər/
A person who makes threats or expresses an intention to cause harm or danger to someone or something.
The police took the threatener seriously and increased security around the area.
Threatener → It is formed from "threat" (from Old English *þreat*, meaning a threat or danger) and "-ener" (a suffix indicating a person who performs an action). The word "threatener" refers to a person who makes a threat or poses a danger.
Think of someone who makes a 'threat' — that's what a 'threatener' does, they are the person who threatens.