The tool is called Ngram and you can see how many times certain words and phrases have occurred in books (English) over the years. The books are those in the Google db so I am sure the data is absolutely correct but it is good enough to get a good trend line representing what is and was going on in our culture.
For example here are what two searches I did this morning provided. The words were terrorism and Jesus.
The tool is here.
About the db:
We constructed a corpus of digitized texts containing about 4% of all books ever printed. Analysis of this corpus enables us to investigate cultural trends quantitatively. We survey the vast terrain of "culturomics", focusing on linguistic and cultural phenomena that were reflected in the English language between 1800 and 2000. We show how this approach can provide insights about fields as diverse as lexicography, the evolution of grammar, collective memory, the adoption of technology, the pursuit of fame, censorship, and historical epidemiology. "Culturomics" extends the boundaries of rigorous quantitative inquiry to a wide array of new phenomena spanning the social sciences and the humanities.