Moby Dick by Herman Melville Chapter 32 Page 10

To be short, then, a whale is a spouting fish with a horizontal tail. There you have him. However contracted, that definition is the result of expanded meditation. A walrus spouts much like a whale, but the walrus is not a fish, because he is amphibious. But the last term of the definition is still more cogent, as coupled with the first. Almost ANYONE must have noticed that all the fish familiar to landsmen have not a flat, but a vertical, or up-and-down tail. Whereas, among spouting fish the tail, though it may be similarly shaped, invariably assumes a horizontal position.

By the above definition of what a whale is, I do by no means exclude from the leviathanic brotherhood any sea creature hitherto identified with the whale by the best informed Nantucketers; nor, on the other hand, link with it any fish hitherto