Words are " a speech sound or series of speech sounds that symbolize and communicate meaning, usually without being divisible into smaller units capable of independent use." This, as you can see, is a dictionary definition, it helps us take a brief glimpse of the concept "word" as it is difficult to define. These "symbols" stand fot things that we want to represent and/or communicate, they can be said or written. They try to describe the world in the way we see or feel it, but at the same time they describe the world in the way our culture sees it. Since words are constructed, they are determined by the time and place we live on, they have a lot of cultural elements. This is the reason someone in China doesn't use the same words as us, and although we can translate them, we need the cultural background to fully undestand them.
Now we can see that words can divide us because some belong to certain places and won't be undestanded by everyone. This can be overcomed by learning the language or key words.
The real division the question is talking about relates to words that are used to insult or segregate. As I said, words are created and some were created with this purpose, using them implies following some beliefs. For example the "n" word was used in the U.S. to segregate the african americans. If someone uses it today we would asume he/she is racist. Some of these words had a very specific purpose to divide and were very powerful having an important role in human history.
