E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
The Latins call me porcus. A sly reproof to anyone boasting, showing off, or trying to make himself appear greater than he is. The fable says that a wolf was going to devour a pig, when the pig observed that it was Friday, and no good Catholic would eat meat on a Friday. Going on together, the wolf said to the pig, They seem to call you by many names. Yes, said the pig, I am called swine, grunter, hog, and I know not what besides. The Latins call me porcus. Porpus, do they? said the wolf, making an intentional blunder. Well, porpoise is a fish, and we may eat fish on a Friday. So saying, he devoured him without another word.