Arabic is made up mostly of 3 letter root words (verbs), these are well known and have not changed since the time of the Quran. Arabic as it is spoken has changed and evolved like any language, but the roots of the language as contained in the Quran have been preserved. Anyone who wants to learn the Arabic of the Quran has plenty of resources. I have a dictionary which defines each word of the Quran, and breaks it down by it's 3 letter root.
This is exactly the same as Hebrew (and Arabic is related to Hebrew), but this does not change the fact that the ancient languages evolve and diverge from the original. In fact, just because a word has a three letter root (with a root meaning) does not mean that a word derived from it keeps its relation to the root. I can explain this using English (though it is not as clean as using the Hebrew to do it).
Let's look at the word "cool" for a moment. It's original meaning is to be something closes to cold, but not quite cold. It's use would be something like, "This nice breeze feels cool on my face." However, in recent decades, the word took on a new meaning. It can also mean "great" or "awesome". An example would be, "This game is really cool!" In this case, the very same word is used, but its meaning is drastically different. In Arabic the same things have happened, as is the case with any language.
Again, just because we can trace a word to its three letter root does not mean we have found the core of its meaning.
