In the course of editing a medical article I came across the phrase in silico, which at first mystified me; fortunately, Wikipedia has an admirably thorough entry that not only defines it—”performed on computer or via computer simulation”—but discusses the propriety of the word-formation:

Contrary to widespread belief, in silico does not mean anything in Latin… “In silico” was briefly challenged by “in silicio”, which is correct Latin for in silicon (the Latin term for silicon, silicium, was created at the beginning of the 19th century by Berzelius). “In silico” was perceived as catchier, possibly through similarity to the word silicate. “In silico” is now almost universal; it even occurs in a journal title (In Silico Biology:

The Wikipedia article also provides a citation for the first use: “Using the data available in libraries […] two sets of experiments were performed on computers (experiments in silico) using the consistency of the data extracted.” (Danchin A, Medigue C, Gascuel O, Soldano H, Henaut A. From data banks to data bases. Res Microbiol. 1991 Sep-Oct;142(7-8):913-6.) I trust it will show up in the OED in due time. (Although generally I prefer that words be properly formed, I have to agree that in silico is preferable to the longer form, and hell, silicium isn’t classical anyway.)


  1. Jim Monroe’s book, Everyone in Silico, is set in a recognizable future with part of the population existing in simulation with the real world. (free and dead-tree versions available).

  2. Justin Neville says

    Strikes me as very similar-sounding to the Italian phrase “in bilico”, meaning “in the balance”…

  3. “In silico” is a parallel with “in vivo” and “in vitro”, the two other places to do biology experiments. Using “silico” instead of “silicio” preserves the stress pattern.

  4. Certainly, sĭlex, silīcis (mf) has been known to Early Romans and their ancestors since—let me make a wild guess—the Paleolithics; the word is indeed in Lewis & Short with attestations to Plautus and Cato the Elder. To do an experiment in “that thing” would be “in silice”, and in the genitive plural (“of flintstones”) it is “silicium”, which, as I am guessing, is the derivation of the name “silicium” for the chemical element.
    This is not yet the end of similarity between “silicium” the silicon and “silex” the flint, and, since they are wildly incognate one to each other in English, Russian—to the rescue—has [krémn^ij], кремний for the former and [krémēnĭ], кремень, for the latter, perhaps formed as кремний

  5. kkm, I don’t think a genitive plural formation is necessary to explain it: it’s just silic- + -ium. Remember, people were regularly writing all sorts of stuff in Latin until very recently, so not everything has to be classical.
    I’m with LH on this one though: I think we can argue that “in silico” is attested and plausible enough that we can say that silicum is an alternate form of silicium. And it’s especially plausible if we interpret the -on of silicon as a greek 2nd declension neuter ending (course I don’t think it really is, but that’s beside the point).
    certain other widely attested scientific barbarities, however, I will not accept in “real” Latin 😉

  6. Luigi M. De Luca says

    “In silico” is an aberration of the classical Latin “in silice”, which conveys the message that the process occurs in a computer-mediated manner, i.e. in a product, the computer chip, made of silicon (Latin “silex-silicis”). As this noun gives us “silice” in the ablative case required by the preposition “in”, the correct Latin expression is “in silice”. The justification for the use of “in silico” is based on similarity of sound to Latin “in vitro”, and “in vivo” both ending in “o”. But this can promptly be discounted by the appropriate use of the equally common use of Latin “in situ” which ends in “u”, indeed the correct ending for the ablative of the 4th declension noun “situs-us”.

  7. Silicium was renamed silicon in 1817 by Thomas Thomson, who recognized that it was not quite a metal, and accordingly gave it the Greek suffix to match carbon and boron.
    So, unless I’m missing something, silicon should follow other Latin nouns of Greek origin ending in -on, and use the second declension, with the ablative in silicō.

  8. For those thinking, like me, that this discussion seems more recent than 2006, there was some in 2019 in the comments starting here.

  9. ktschwarz says

    Hat 2006: “I trust it will show up in the OED in due time.”

    In silico entered the OED as a draft addition in June 2015 under in, prep.2 (the Latin preposition, in Latin phrases used in English), with a first citation from 1987. Wikipedia now has more detail on the earliest uses.

    Merriam-Webster must have entered in silico by 2013, since they featured it on a Word of the Day podcast in that year. They have it dated 1992; I’m guessing they don’t count technical and specialist publications, since their first citation is from Newsday.

    In vitro and in vivo were coined at the end of the 19th century, too late to make it into the OED’s fascicle I-In (1899). They were included in the 1933 supplement.

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