orca vs killer whale

orca and killer whale both are nouns.

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

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

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

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

orca (noun)	killer whale (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