Oh, quite often (but indeed not always), there is a way to tell! And in the case of the word 'cat', it can be substantiated that it is certainly not a Germanic word originally, but a loan from, or rather via, (Late) Latin. 'Late' because a few very typically Germanic sound changes didn't work at that moment anymore. I read about two possible origins, viz. a Celtic or a North-African origin for the word.b dude has a point, there is no way to tell whether a very basic word has been borrowed from latinate into germanic or vice versa, such as 'cat' and 'two.'
- Germanic: via Latin, prob. from Celtic."i drove my wagon off a cliff with our ugly friend as the lights went out all over my little town. I can not understand why writing only in Germanic words is so hard. if the words have sister words in Dutch, Swedish, Norwegian, German, then they are from the good old English tongue, before it was undone by the Gauls."
Frank
PS: I hope this is not regarded as nitpicking. I just love to look up these kinds of things. And as written before, i wouldn't like to write even a short "Germanic-only" note in my (Germanic) native tongue Dutch.