I read an article recently where the author used "substract" instead of "subtract". I'm more familiar with the latter word but after doing a bit of googling, it seems that both words are being used, although "subtract" seems more mainstream than the other. Which of the two is more appropriate? Is "substract" even acceptable?

  • How about some old text books on mathematics/arithmetic? I feel I have something to say on this. Did they use substract, with the additional "s"? – Kris Nov 24 '11 at 9:44
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    @Kris: As old dictionaries show (see my answer), "substract" was already considered erroneous and obsolete in 1891 and 1913. So you'd have to consider books much older than that, if at all. – ShreevatsaR Mar 2 '12 at 15:09
  • @ShreevatsaR I did not mean that old! I'm sure it existed in the sixties though I could not dig up any references. – Kris Mar 3 '12 at 11:03
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    'substract' sounds better, but we are more familiar with 'subtract' so this creates confusion which should not be there. – user44175 May 13 '13 at 15:21
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    @vicks: I think subtract sounds better. Maybe the entire mathematical world should go to war over this. =) – Kaiser Octavius Jun 25 '13 at 13:17

"Subtract" is the word. Though the obsolete word "substract" did exist, any occurrence you see these days is most likely just a common mistake, formed by analogy either with "abstract" or with other languages whose corresponding words do have two ‘s’s.

Many recent dictionaries do not list "substract". Of "substract", the Century Dictionary (1891) said:

  1. An erroneous form of subtract, common in vulgar use.

Webster's Revised Unabridged Dictionary of 1913 called it "obsolete", while the even older version of 1828 said

Note.--Substract was formerly used in analogy with abstract. But in modern usage, it is written according to the Latin, subtract. See this word and its derivatives.

Additionally, I know people who find "substract" very annoying. :-)

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    It is annoying, isn't it? – Jonn Oct 4 '10 at 6:33
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    I didn't claim to be one of them. ;-) – ShreevatsaR Oct 4 '10 at 6:35
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    I'm probably one of them though. XD – Jonn Oct 4 '10 at 10:51
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    last two links are broken! – Visruth Nov 5 '17 at 17:33
  • Apparently I don't have sufficient rep to post, but according to Merriam-Webster, substraction does have a legitimate history, as well as a secondary, non-mathematical sense. It also cites a different etymology than those given in other answers (without reference), here: "Medieval Latin substraction-, substractio, from Late Latin substractus." Would be nice to see word lovers role model tolerance, curiosity & appreciation of differences... – Rax Adaam Feb 22 at 1:24

It seems that the usage of "substract" is linguistically incorrect. However, I disagree about explaining this usage as a "showing-off". It seems that other languages do contain the letter "s" as in "soustraction" in French. People with a multi-lingual background are more likely to make mistakes, and it is nice if we just point that out to them without prejudice.

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    But that's because "sous" means "sub". "Souterrain" must've lobbed it off to make it sound better. – Cees Timmerman Nov 12 '13 at 18:58
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    .. because "souterrain" is a composed word from "sous" and "terrain" where "sous" has its last letter '-s' mute. – Vincent Jul 4 '17 at 6:34
  • @CeesTimmerman That is probably true. In old texts souterrain is written as soûtterain, where the circumflex indicates the lobbed-off 's'. Also, the correct word "substrate" might cause additional confusion. – wensveen Aug 23 '19 at 10:12

French people use "substract" mistakingly a lot because in french, the word is "soustraction", which contains the sound "s" inside.

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    Same in Spanish and Galician at least. We tend to assume that "substract" is correct because of "sustraer" in our language. English "subtract", Spanish "sustraer" and French "soustraire" share a common root, but an epenthetic "s" was probably added for the Latin-derived languages at some point. – CesarGon Jul 17 '12 at 18:38
  • I'm surprised a completely unsubstantiated statement like this is not flagged or removed by moderators... This is nothing more than a plausible generalization, but hardly useful. – Rax Adaam Feb 22 at 1:16

If substract is incorrect according to established English usage, this is only because English usage derives this verb from Latin subtraho ‘to subtract’, which excludes the ‑s‑.

In many a Romance language — for example, in Spanish — it derives from the Latin prefix sub‑ coupled with the Latin verb extraho ‘to extract’; hence Spanish substraer. You say ‘sub-tract’ in English where in Spanish we say ‘sub-extract’; hence the extra s.

Substract is incorrect in English, but it could equally have been correct if imported differently.

  • Is "ex" actually the source of this s, or is it possibly just epenthetic like the s in "abstract"? – herisson Oct 1 '15 at 4:18

I've never heard of "substract" and, more to the point, neither has my edition of the Oxford English Dictionary. Even if it is a word, assuming that it means the same as "subtract" I can't see any point in preferring it over the better known word, apart from showing off.


By looking at the etymology, we can see that "substract" is erroneous. "subtract" is derived from a the Latin compound verb "subtraho", whose supine is "subtractum". There is no form "substraho" of this verb.


I found the word "substract" in a memoir written by an old Boston lady in the 1920s, describing how she as a child (during the 1850s) pilfered newspapers from her mother's cache and was able to trade them for candy. I like this usage, as it conveys a kind of arch, sneaky tone better than either "extract" or "subtract" But it's not mathematical at all.

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    Interestingly, the word "abstract" is itself used in such a sense: to pull out something, or even to pilfer. – ShreevatsaR Nov 6 '12 at 6:44

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