Apparently, all these words, jam, dog, big, fun and bad are unrelated to any other and have unknown origins, so it says in the newspaper today. However, it does seem that dog might come from the Old English word dogca, but it suddenly sprang into use in the middle ages replacing hound, which had been used before… no-one seems to know why. Jam is another word… we usually think of two senses, to jam something in as in push or squash, or jam which is made from fruit… could it have come from champ which means to chew? It doesn’t seem likely, more like a coincidentally similar sound.
So what about big? Bigge is a Scandinavian word meaning strong… so maybe the Vikings and other invaders brought it. Fun? Could that come from fon, meaning to fool? As for bad, no-one has the least clue where that came from and it doesn’t relate to anything else, except a word which means weak but that really isn’t the same, is it?
Jam, dog, big, fun, bad… That’s what is so interesting about English!
Lois Elsden 