How did 东西 come to mean "something" in the expression "吃东西"? I was chatting with a Chinese penpal recently and when I asked "what are you doing?", I received the following answer:


  吃东西，你呢？


Now, "东西" means "east and west" and so "吃东西" literally means "eat/eating east and west".

After I asked for explanations, I got this reply "I am eating something". The explanation included the fact that this depends on context.

So, how did 东西 come to mean "something"? And in what contexts can it be found with what meanings?

If the list is long, include only the most famous cases (5, 10 cases).
This is a good question about etymology of Chinese word. Most native speakers are not interested in etymology as they can speak out of habit while non-native speakers are more curious on how the sense of words evolves. Back to your question, there are nice articles on both Wikipedia and Baidu Baike that explains the etymology of "东西". Since there are acutally quite a few explanations for this one, so I cannot translate them all here. But I can help you if you have trouble to understand particular sentences.