What the Hell Have I?

I read a line in a novel today that said words mean things, and that got me to thinking. Words don't really mean anything, except by mutual agreement. I'm sure I'm not the first person to mention this, not by a longshot, but it's the first time I can remember really thinking about it. Words don't mean anything unless people agree that they do. Otherwise, they're just sounds or squiggly marks. I mean, if you meet someone who doesn't speak the same language that you do and you convey to them that the sound "carrot" means a vehicle with an internal combustion engine that you drive around, how are they to know different? To take it a step further, let's look at two words that don't seem to have anything in common--A chair is something you sit in, right? And a head is something that sits on top of a neck and contains a brain. These two words don't seem to have anything to do with one another. And yet, isn't the chair of a committee the head of that committee? Yeah, it's weird. Maybe I just have too much time on my hands. Anyway, maybe it's all the seed of a story that I'll never write.