killer whale vs Orcinus orca

killer whale and Orcinus orca both are nouns.

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

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

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

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

killer whale (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