dog

Few common English words are as mysterious as dog. It appears in Old English as docga, but where docga itself came from, nobody knows — it has no clear relatives in other Germanic languages. The older, 'official' word for the animal was hund (modern hound), the word German and Dutch still use (Hund, hond). Somehow the obscure slang-like docga pushed hund aside and became the everyday term, while hound narrowed to mean a hunting dog. This is the rare case of a basic, ancient-feeling word with a completely unknown birth.

Because the dog has lived beside humans for so long, the word grew a layer of metaphor. A dog is loyal and won't let go of a bone — so dogged means stubbornly persistent, and to dog someone (verb) is to follow them relentlessly, the way a hound trails a scent. A dog guards the house, so a watchdog is anything that watches for wrongdoing: a press watchdog, a financial watchdog. And because dogs were seen as low and rough, doggerel came to mean clumsy, sing-song verse — poetry 'fit only for dogs.'

Notice the pattern: these are not Latin prefixes bolting onto a stem. They are plain English compounds and figures of speech built on one vivid animal. The 'root' here is really a picture — the faithful, dogged, ever-trailing dog — and each word borrows one trait of that picture.