Google has digested over 15 million books to date and has come up with an interesting way to plot the usage of words over time. Ngrams are line charts that show the usage of words over time. Try some neologisms, like 'went missing' , which is relatively new to American English or laser, etc., to track when they came into everyday use. You can also pick two words to compare and you get to decide the time-line.
It does not filter out any words, including four letter words. It also has proper names. Think about interesting words and see how they relate to each other. There is a timeline on the bottom that lets you click to read the books used in the analysis. It is a fun way to pass some time and may be a site to bookmark so you can go back when a new word intrigues you, like extoplasm.
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