Google Books Ngram Viewer

Graph these comma-separated phrases:
case-insensitive
between and from the corpus with smoothing of .  
Search in Google Books:

1800 - 1815 1816 - 1838 1839 - 1849 1850 - 1965 1966 - 2000 oppressor English
1800 - 1824 1825 - 1826 1827 1828 - 1939 1940 - 2000 oppressour English

Run your own experiment! Raw data is available for download here.
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