killer vs Orcinus orca

killer and Orcinus orca both are nouns.

Word	Noun	Adjective	Verb	Adverb
killer	Yes	No	No	No
Orcinus orca	Yes	No	No	No

As nouns, killer and Orcinus orca are synonyms defined as:

killer and Orcinus orca: predatory black-and-white toothed whale with large dorsal fin; common in cold seas

Other synonyms of killer include grampus, killer whale, orca, sea wolf.

killer (noun)	Orcinus orca (noun)
predatory black-and-white toothed whale with large dorsal fin; common in cold seas	predatory black-and-white toothed whale with large dorsal fin; common in cold seas
a difficulty that is hard to deal with
someone who causes the death of a person or animal
the causal agent resulting in death