Google Ngram Viewer
The Google Ngram Viewer or Google Books Ngram Viewer is an online search engine that charts the frequencies of any set of comma-delimited search strings using a yearly count of n-grams found in sources printed between 1500 and the present.
The program can search for a single word or a phrase, including misspellings. The n-grams are matched with the text within the selected corpus, optionally using case-sensitive spelling (which compares the exact use of uppercase letters), and, if found in 40 or more books, are then plotted on a graph.
“In the fields of computational linguistics and probability, an n-gram is a contiguous sequence of n items from a given sample of text or speech. The items can be phonemes, syllables, letters, words or base pairs according to the application. The n-grams typically are collected from a text or speech corpus. When the items are words, n-grams may also be called shingles.”