The word dog is something of a mystery.

All of English’s relatives have something like hound: German has Hund, Dutch has hond, Swedish has hund.

Yet only English has a word like dog.

In Old English, the word for ‘dog’ was hund too, a word which survives in hound. It's traceable back thousands of years to link up with its cousins in Latin canis and Ancient Greek kýōn.

Then, around the year 1050, a different word appears: docga.

It’s clearly the ancestor of dog. But it has almost no written history before that, and no clear relatives in any other language.

Nevertheless, by 1500, dog had replaced hound as the normal word for the animal. The upstart won: a real “underhound story.”

So where did dog come from?

Some scholars think it might be a nickname. One clue: dog belongs to a cluster of English words that all share an unusual shape.

We have dog, pig, stag, frog, hog, even earwig.

They're all terms for animals, the kinds of things we might give cute nicknames to… even earwigs.

On this theory, these words are like thousand-year-old versions of doggy and piggy. They tend not to show up in Old English texts because they're informal: not the kind of thing monks write about.

That's one theory, anyway: we'll probably never know for sure.