Listen here, philologists amateur and professional: Google Ngrams are highly groovy. You can check the relative usage of particular words over a 500-year period - and also compare British v American English.
For example, ruthful blips up in the 1580s before succumbing to its ruthless antonym.
And here you'll note that connexion was really quite competitive with connection until the 1850s (indeed, it was winning in the early 19th century):
Those are things I've discovered in a few minutes of playing around. Let me know if you discover anything cool!
Also available for French, Spanish, German, Russian and Hebrew.