“The killer whale or orca is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member.

The toothed whales are a parvorder of cetaceans that includes dolphins, porpoises, and all other whales possessing teeth, such as the beaked whales and sperm whales.“

So, yes, in the sense that sperm whales and porpoises are also dolphins, it too is a dolphin. but that’s not typically how we use the word dolphin.