According to google, Etymology is the study of words and they way they have change their meanings throughout history. I'll give you one example. The meaning of atheism according to most popular belief is "I lack belief". Most atheists will agree to this. However, the Etymology and the historical meaning of atheism is no god (a-no, god- theos) that is the claim of atheism. It does not mean lack of belief. This idea of lack belief is the new meaning and quite popular in the atheist community.