When looking only at the related forms that mean "3", and comparing all six languages, the one that differs most from the other five is English.
The number 3, in English, is spelled "three". When compared to the other languages ("trois" in French, "tres" in Latin, "tri" in Celtic, "treis" in Greek and "tri" in Sanskrit), it can be understood as the most different one, because there is one letter that isn't part of the words that mean "3" for the other languages: that would be letter "h". Letter "h" appears right before the letter "r" in the word, which doesn't happen to the words from the other languages. All of the others present letter "t" followed by letter "r", and all of them have variations of the letters "i", "e" or "s". There is no presence of both letters "i" or "s" on the word "three" in English either, which makes it even more different from the others.
