What is the difference between the two adjectives periodic and periodical?

For instance should I say "a periodic event" or "a periodical event" ?

closed as off-topic by user3169, Nathan Tuggy, Eddie Kal, Hellion, Andrew Oct 22 '18 at 14:21

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  • Some example sentences using these words should be added to your question to suggest actual usage. Otherwise, this is just a dictionary exercise. – user3169 Oct 20 '18 at 22:55

As adjectives, they are treated as synonyms.

According to ngram, "periodic" is more common in modern English. Because "periodical" in modern US English is used as a noun about one third of the time, the reasonable inference from the ngram data is that today "periodic" is far more common an adjective than is "periodical." If you want your English to appear current, at least in the US, I recommend using "periodical" only as a noun.

EDIT: Thanks to Laurel's helpful hint on how to do a deeper analysis with ngram, I have edited my comment above. The edit does not change the basic conclusion.

  • 1
    Why not just look at the Ngram data for the adjective version of both words separately? And ditto for the noun versions. All the popular Ngram software I'm familiar with has this feature. – Laurel Oct 20 '18 at 22:27
  • @ Laurel Because I did not know that you can do that. Thanks – Jeff Morrow Oct 21 '18 at 0:04

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