If you search the web to determine the etymology of the phrase piggy bank, you'll quickly conclude that there is little disagreement over its origin.
Many web pages give the following story: There was once a kind of clay called pygg. People made containers out of it, and they put money in some of those containers, which became known as pygg jars or pygg banks. Because pygg began to sound like pig, people started making those banks in the shape of pigs, so by the 18th century the term had become pig bank, which later turned into piggy bank.
That's a nicely satisfying story. Only trouble is, I don't believe it.
It sounded too pat to me; it has the feel of folkloric etymology. And as linguists like to say, etymology by sound is not sound etymology. It didn't sound impossible to me, just implausible.
So I did some research. In particular, I checked two dictionaries that I find generally reliable for etymology: Webster's Third New International Dictionary, Unabridged (MW3) and the Oxford English Dictionary (OED). Both implied that piggy bank derived straightforwardly from pig.
So I poked around online some more, and I gradually concluded that most of the web pages that provide the pygg story got their info from a Straight Dope column titled What's the origin of the piggy bank? Usually I find Straight Dope pretty reliable, but in this case I think Science Advisory Board member Mac may've been too trusting of the single source that they seem to have consulted, a 1989 book called Extraordinary Origins of Everyday Things, by Charles Panati.
I used online resources to look at the Panati book. Sure enough, in the chapter titled “At Play,” it gives the pygg story. So I checked Panati's references section for that chapter to see where he got the info. Unfortunately, none of the listed references seems relevant to piggy banks, and the ones that are searchable through Google Books don't seem to mention piggy banks or pygg.
I also looked at a different research path: Panati says pygg was called that during “the Middle Ages,” and Straight Dope talks about the Great Vowel Shift, and various other sources claim that pygg was a Middle English word. (People who pick up this story do seem to like to elaborate on it.) So I checked the online Middle English Dictionary. I can't find any evidence there that pygg was a type of clay; all the cites of pygg in quotations are variant spellings of pig and clearly refer to the animal. Could Panati have meant it was an Old English word or an early Modern English word instead of Middle English? I suppose, but there's no listing for pygg in the online Old English dictionaries I checked, nor in MW3. The OED lists pygg(e) as an obsolete spelling of pig; it doesn't say anything about clay.
Meanwhile, I dropped a note to the Merriam-Webster etymology people asking about this. (I think it's totally awesome that you can ask them etymology questions.) I soon got back a response from Etymology Editor Jim Rader, who wrote, in part:
[...] the story about 18th-century "pygg banks" looks entirely fictional to me. [...] piggy banks [...] appear to have originated in the U.S. not much earlier than the 1890's. Google Books does not turn up any cites of pig bank in the relevant sense before 1902, or of piggy bank before 1909. A search of other data bases might produce something earlier, but these dates seem indicative enough.
(Quoted here with his permission.) I kicked myself for not having thought to check Google Books myself.
So although the pygg story is extremely widespread, I can't find any evidence for it from a reliable source. To recap:
- I can't find evidence that there was ever a kind of clay called pygg.
- I can't find evidence that there were things called pig banks before the late 19th century.
- I can't find evidence that pig banks were named after anything other than their resemblance to pigs.
I'll try and find out more about Panati's source for the story, but at this point I'm inclined to chalk it up to folklore.
If any of you have any further insights or references, let me know.