Why is series both singular and plural in English? In the other languages I am familiar with, serie is the singular. This includes Spanish, French, German, and Italian.

However, it is series (in a row) in Latin , although I have also seen the singular used in some texts.

The only source (Webster’s 1913 edition) that mentioned serie in English use says it is an obsolete form.

When did it become obsolete? Going back to 1600, Ngrams is essentially useless in this case.

  • Bear in mind that, prior to about 1850, dictionaries did not exist as an authoritative description of English spelling and definitions. Writers and printers used whatever spelling 'felt right" to them. In the particular case of "series" things also get confused because, by definition, the word refers to a plurality of items, even if there is only one series.
    – Hot Licks
    Jan 28, 2019 at 23:24
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    It needs to be noted that one must now be wary of using the word "serie", lest it unintentionally provoke a response from from your iPhone.
    – Hot Licks
    Jan 29, 2019 at 3:59
  • Regarding "although I have also seen the singular used in some texts", the noun series is fifth declension, so the nominative case of the singular is series, but the ablative case in Latin is serie. So the Latin for "in the series" is in serie. Sep 18, 2022 at 17:22

2 Answers 2


My impression is that "serie" is not exactly "obsolete" so much as it is more stigmatized now than it was in the past (maybe a similar example would be the use of "I" in contexts like "between you and I"). Although I associate singular "serie" with non-native speakers, I believe it is also used by some native English speakers in the present.

It's not clear to me that serie was ever the usual form of this word in English. The Oxford English Dictionary has examples of singular series from as early as 1618. The OED entry for serie says "Often criticized in usage guides from the mid 20th cent. (and earlier in N.E.D.: see quot. 1884) as incorrect or nonstandard, and still not common."

As you mentioned, series is used as a singular in English because that is the singular form of the word in Latin. There are many words where English uses a fully Latin spelling but French or another Romance language uses an adaptation: e.g. English thesis vs. French thèse or Italian tesi.

  • Actually thesis might not be a good example of a Latin word.
    – Andrew Leach
    Jan 28, 2019 at 19:04
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    @AndrewLeach: thesis was taken into English from Latin. The Latin influence can be seen in the plural form, which is theses and not e.g. "theseis". Its ultimate origin being Greek doesn't really make a difference to my point as far as I can tell.
    – herisson
    Jan 28, 2019 at 19:11
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    OED doesn't mention Latin at all: "Etymology: < Greek θέσις putting, placing; a proposition, affirmation, etc., < root θε- of τιθέναι to put, place."
    – Andrew Leach
    Jan 28, 2019 at 19:13
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    @AndrewLeach: the etymology section of that entry is pretty short and doesn't mention Latin, but consider the context of the earliest citations, such as a 1398 translation of the Latin work "De proprietatibus rerum". There are some English words from Greek that were not transmitted via the medium of Latin (I think "koine" is an example), but it seems very unlikely to me that thesis is one of those. Note also that I didn't actually say it is a "Latin word", just that it is a Latin spelling.
    – herisson
    Jan 28, 2019 at 19:21
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    What about usage of the term “in serie”? There seems to be some support for this, analogous to in specie (ignore the references in the link to “Series A” and the like).
    – Lawrence
    Jan 29, 2019 at 2:55

The complete Oxford English Dictionary reports several things of note. First, that despite first appearing (with the meaning you use) in the written record in 1840 serie has been criticised since at least 1884 as being non-standard usage. Additionally, there is a quotation from 1940 pointing to the "mistaken" use of serie and specie.

From those observations I think one can reasonably conclude that serie was always non-standard in British English and that it became obsolete almost as soon as it appeared.

Noteworthy is that in Chaucer's Knight's Tale, the word serie appears with a slighly different meaning, and again seems to have become obsolete almost immediately.

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