A pair of orcas.
orca definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
orca definition by American Heritage Dictionary
See killer whale.
Origin: Latin ōrca, whale, probably alteration (probably influenced by ōrca, vessel) of Greek orux, orug-, pickax, a kind of large fish or whale, perhaps from orussein, to dig.