Language (words) are a means of communication. They're symbols really, to represent objects, ideas, concepts; and to be useful, it has to be understood by all parties communicating. 

But that's where the problem comes in. People comprehend ideas and concepts quite differently though they might have a 'general' meaning, but still we use the same language to express those similar yet different ideas. That is why the meaning of words and language changes with time, context, and very importantly, individual comprehension and belief. 

Take as example, when you hear the word 'gay,' your first thought is most probably about homosexuality, but centuries ago your first thought would have been 'happy', or maybe 'carefree' and 'promiscuous' as the word evolved. This is just an example of change in language meaning with time. 

But even in the same time, language could have different meanings for different people. If someone says (asks): do you believe in God? There are problems with this question. First, what does he mean by 'God.' You might not believe it (and I won't be surprised) but people have very different conceptualization of what (or who) God is. For some it is a Supreme being who created the world, split the red sea through Moses and sent the savior, Jesus; for another it could be the supreme being who created the world, split the red seas but didn't send any savior (or at least, not yet); for some it's what they find most important, like money; or it could be Zeus, or Sango. They're not the same thing. Then there's another question, what is belief? One could say he believes in something but his actions doesn't match, does he really believe? Believe? but to what extent? 

This ambiguity of language is very risky, especially in legal matters. One word or sentence could have different meanings, and that is one of the reasons people hire lawyers--to eliminate (or infuse, maliciously) these ambiguous terms. In all as I've said, it does stresses me, because, I think, if you're quite observant, you would notice it quite commonly in communications. They cause misunderstanding between people.

I've been thinking about what the reason could be, why does ambiguity exist in our language, why does it change with time? Why can't we just decide what a particular word means and stick with? I don't really know, but my first thought was that anything created by humans is cursed with imperfection. It could also be that our thoughts are just too different for our limited vocabulary to capture and it is not actually useful to create a word for whatever variation of an idea every person could have. I've forgotten many other possible reasons I thought of.

Finally, I hope that this has made you (the reader) become more aware of the ambiguity of language and how it could be problematic. I do try to eliminate this in my conversations with people by asking questions about what they really mean when they say something whose meaning is not quite clear to me. Clarity saves.