Definition of "blue whale"

But there are a rabble of uncertain, fugitive half-fabulous whales, which as an American whaleman, I know by reputation, but not personally....the Iceberg whale; the Quog Whale; the Blue Whale. But I omit them as altogether obsolete and can hardly help suspecting them for mere sounds full of leviathanism, but signifying nothing.

1851, Herman Melville, Moby Dick, page 131