The Google Books Ngram viewer is a database that allows you to search for words or phrases in the 25 million plus books scanned in Google Books.
You can use this to search see how often your word was used in published books during a certain time period. Remember, you can click on the links below the graphs to search Google Books. See a spike in usage? Try to figure out what's going on during that time period!
JSTOR is an archive of scholarly journal articles and eBooks from a wide variety of disciplines (from the sciences to the humanities to the arts), with journal coverage dating back to the 1800s. The most recent two to five years of a journal may not be included, however.