the causal agent resulting in death
"heart disease is the biggest killer in the United States"
predatory black-and-white toothed whale with large dorsal fin; common in cold seas
"The captain ordered everyone to lower their binoculars as a killer breached near the bow, its massive dorsal fin slicing through the icy waves."
One who or that which kills.
"The silent killer moved through the shadows without making a sound before taking its final breath."
In plain English: A killer is someone who intentionally takes another person's life.
"The killer was caught after he tried to flee the scene."
Usage: Use "killer" as a noun to refer to a person or thing that causes death, such as a murderer in a crime story or a machine that destroys pests. Avoid using it for exciting events unless you are specifically describing an object designed to eliminate something harmful.
Excellent, very good, cool.
"That new restaurant has killer burgers and an amazing view."
In plain English: Killer means extremely good at something, like being amazing at playing a sport or winning games.
"The killer heatwave made everyone stay inside all day."
Usage: Use "killer" as an adjective to describe something that is exceptionally good, exciting, or impressive, such as calling a movie a killer film. Avoid using it in formal writing where "excellent" or "superb" would be more appropriate.
The word killer comes from Middle English and was formed by adding the suffix "-er" to the verb kill. This straightforward construction indicates a person or thing that performs the action of killing.