Tangled up in words

Language is suppose to help communication I thought but some words are too similar. I was enthusing on about place that sold free trade goods until I listened to myself. I didn't mean free trade, I meant fair trade. How come two such different concepts, with such different ramifications are so similar? Just as well I am not in some trade negotiation, I could agree to anything.
How come awful apparently used to mean full of awe and now means horrible? While awesome, which surely having only some awe is less than being totally full of awe, gets to mean awe-inspiring?
How come a marketer thought it was smart to have a shop sign that said half price, half shop? The two "half" words underneath one another so the poor shop assistants had to explain to every customer that only half the things in the shop were half price, not that it was a half price shop which your brain automatically registered it as.
I listen to my children trying to get their head around a language where you can have "yours" but not "mines" and you can have "listened" but not "heared".
And I still think alot should be an acceptable compound word.