What is the latin prefix for "2½ times" ?


  • The question asks for the correct analogue of the prefix "sesqui-" which, of course, is the prefix for "1½ times".
  • 2
    There is a decent chance that there is no such prefix at all. After all, we are extremely unlikely to have a separate prefix for 13½ times or the like, so the prefix sequence (semi-, sesqui-, ...) has to terminate somewhere. Whether 2½ is included is a good question.
    – Joonas Ilmavirta
    Commented Aug 7, 2017 at 18:01
  • Many thanks for the answers. There was a precise motivation for this: it can be useful, to give structure to investigations, to have words for the number of syllables in (the usual spoken rendition of) a word, and yes, half-syllables are on the radar of science, and yet I do not know of any usual term for 2½-syllabic. In particular "sestersyllabic" is (probably not for long because of this thread) currently an example of the rare species of reasonable words with 0 hits on G.
    – guest
    Commented Aug 8, 2017 at 6:56

3 Answers 3


There is a very common word in Latin that literally means "two and a half": sestertium, -i. This comes from semis + tertius, the idea being (I suppose) that it is "half-way to three [from two]."

This usage is antiquated and almost entirely replaced by the current meaning of a "serterce," which according to L&S is:

a small silver coin, originally equal to two and a half asses

L&S also quotes sestertium as meaning "two and a half feet [deep]," as used by Columella in De Arboribus:

ipsum agrum sat erit bipalio vertere: quod vocant rustici sestertium. (1)

...but this seems like sloppy research to me, since the sentence that immediately follows suggests a number more like 1 2/3:

...Ea repastinatio altitudinis habet plus sesquipedem, minus tamen quam duos pedes.

If you wish to use a prefix for "two and a half" then, you could feasibly go with sester-. It turns out that this phrase already has some traction, for instance as applied to a 250 year anniversary: "sestercentennial". See, for example, this New York Times article, this Wikipedia article, and ~28K Google results. These are all decidedly non-authoritative.


The above-cited Wikipedia article offers one other alternative that fits this case: semiquin-, which means "half of five."

A Word of Caution

The ultimate answer to your question is that there is no frequently used, easily understood prefix for "two and a half." This is probably because (!) it's not a terribly useful thing to have.

Classical attestations of any of the above suggestions are conspicuously absent, whereas we have from Varro a very clean example of what a Roman might have done when faced with the same question. Does he use "sesterpedis" to refer to a two-and-a-half-foot distance? Let's look:

...tympanum in latitudinem duo pedes et semipedem, in altitudinem palmum. (Varro, Res Rusticae

So much easier to understand!

  • 2
    +1 for completeness
    – Rafael
    Commented Aug 7, 2017 at 21:02
  • 1
    Many thanks for this. For motivation, see my comment under the OP. Do you agree that, when used with care, sestersyllabic is a reasonable coinage? ("semiquinsyllabic" seems not as good, both because first going to 5 and the halving is an overcomplication, and because it is longer.)
    – guest
    Commented Aug 8, 2017 at 7:00
  • 1
    @guest I suppose it is reasonable. Out of curiosity, what could you possibly be referring to? Isn't syllable count discrete?
    – brianpck
    Commented Aug 8, 2017 at 13:22
  • @brianpck: for 1½ times this is already in use, and I need to use it for words with 2½ syllables.
    – guest
    Commented Aug 9, 2017 at 19:53
  • For what it's worth, sesqui- and the other prefixes are literal and additive ("½ and a ~") so sester- would more likely be something like "½ less than 3" in the manner of Latin's 18 and 19 rather than "half the distance from 2 to 3".
    – lly
    Commented Jun 16, 2023 at 4:19

The answer could be 'hemipenta' (half of five) as in hemipentahydrate meaning 5 water molecules of crystallization per two molecules of compound. This is cumbersome and probably Greek rather than Latin root per se, but seems it is the related term to Monohydrate 1 water per molecule, Sesquihydrate 3 waters per two molecules, Dihydrate 2 waters per molecule and Trihydrate 3 waters per molecule. Anyway it appears to be in current chemical use for the hydration ratio of 5:2.

  • 1
    Welcome and thanks for the post. It is Greek indeed, but it's still good information to have.
    – cmw
    Commented Jan 17, 2022 at 13:16

A table of numercal prefixes is given in Wikipedia; both cardinal & multiple forms. What we are duscussing here is the muliple form. Perhaps surprisingly, there is one for 1¼, which is quasqui. So perhaps one could use biquasqui for the 2½ multiple prefix.

But as for sester, I've also read of that one - I can't remember where now; but whatever the writing was that said it, it simply said without qualifcation it is the prefix, whereas a previous respondent speculates that it might be admissible. However, it is not in the Wikipedia table. I do use it and am going to continue to do so, anyway!

The previous respondent also says it's use-potential is borderline (not verbatim). As I said, I do use it; and I find that opportunities for doing so are not extremely rare. As for sestercentenial: an alternative there, as in the same table quater is given for the ¼ multiple prefix, would be quatermillenial.

There is perhaps no precedent for concatenation of bi & another prefix ... but concatenenation of it with any other of these multiple prefixes known to me would result in an elementary redundancy. It does so even in the case of quasqui if sester be admitted. And given quater, the concatenation hemisemi, as in hemisemiquaver in music, is similarly a redundancy.

As for the idea of 'half a syllable': I think that arises in connection with a word such as 'Popocatapetl', or 'Lyublyana': in the case of the former, a native Mexican will pronounce the '-etl' at the end as a single syllable, whereas an English speaker tends to make two syllables of it, but with some effort might be able to get it close to being a single syllable - perhaps a sesquisyllable; and likewise in the latter case - that of a native Slavonic speaker, & the 'Lyu-' & '-lya-' in 'Lyublyana'.

  • 1
    Welcome to the site! Do you happen to have any examples of bi- being actually used to multiply a prefix, as in biquasqui-? I'm not sure that would be interpreted correctly.
    – Joonas Ilmavirta
    Commented Oct 28, 2018 at 9:05
  • Yeah, no. quasqui- isn't multiplictive. It's additive: ¼ and a ~. The equivalent format would be quasquibi-, not biquasqui-.
    – lly
    Commented Jun 16, 2023 at 4:06

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