The "True Meaning" of a word is what society has agreed upon. Society. Meaning, most people. Language is a fluid thing that changes. If bob is a cuss word in 200 years, it is a cuss word in 200 years. You can't point at a previous meaning if the intent is clear, and people agree upon that a certain word means that.
Although many words are used as a matter of course every day, many people could not tell you what the meanings of those words are. If a group of people was asked to provide a definition for certain words it is doubtful that they could do so. They use words out of habit rather than using them because they know and appreciate their true definition.
Honestly, I may not know much about languages and words, but I think I should at least have a saying on this. At least 10%, freaking 10% is the percentage of how we communicate using words. The rest comes from body language, tone (angry, sad, etc.), and facial expression. Though I'm not going into details about the percentages (since I'm lazy like that), the word a in English can mean something totally different in another language. For example, a can be used to show a surprised expression verbally in Chinese. Maybe I would've said yes if the whole world spoke in one language, but that's not the case. Another example would probably be like me saying hey to someone. I could yell, "hey!" with an angry expression on my face, and people would see that I'm mad about something. Or I could maybe say, "hey" in a normal range with a smile, as to get a attention of a friend of mine. Well, I honestly love this site so much because all of the peoples' opinions can be stated here, and sometimes it even changes my opinion.
Some people might be something akin to walking dictionary, but most of us just use the context of surrounding information to deduce the true meanings of words. Even using deductive reasoning doesn't always ensure an understanding of a word, however it usually does the trick. Language, after all, is an ever-changing tool, so I think this is exactly the way things should be.
Even though people use a lot of different words in their everyday speech, they don't really know the exact meaning of most of them. Very few people look up the meaning of a word in a dictionary so there's no way for them to learn what the words mean. People learn how to use words in context by listening to others, so there's little opportunity to learn the exact meaning.
Many people use words loosely without fully understanding their meaning. This leads to hurtful feelings, or worse. It stems from a lack of reading. Video games and television are a wonderful distraction and provides entertainment, but reading is also wonderful and improves vocabulary and imagination. Using words properly is also a sign of intelligence.