killer vs causal agent

killer and causal agent both are nouns.

Word	Noun	Adjective	Verb	Adverb
killer	Yes	No	No	No
causal agent	Yes	No	No	No

As nouns, causal agent is a hypernym of killer; that is, causal agent is a word with a broader meaning than killer:

killer: the causal agent resulting in death
causal agent: any entity that produces an effect or is responsible for events or results

Other hypernyms of killer include causal agency, cause.

killer (noun)	causal agent (noun)
predatory black-and-white toothed whale with large dorsal fin; common in cold seas	any entity that produces an effect or is responsible for events or results
a difficulty that is hard to deal with
someone who causes the death of a person or animal
the causal agent resulting in death