This data was compiled from the Google Books Ngram Viewer data, particularly
the 2012 English dataset.

The data is available from https://books.google.com/ngrams. The terms of use of
this data are:

"Ngram Viewer graphs and data may be freely used for any purpose, although
acknowledgement of Google Books Ngram Viewer as the source, and inclusion of a
link to http://books.google.com/ngrams, would be appreciated."