Can someone help me in understanding the suffix -tor and -ter?

I am not able to understand it properly and I always mix the spelling like:

  • "computor" when it should be computer
  • "administrater" when it should be administrator
  • I don't know that there's a rule for this.
    – Daniel
    Commented Jun 14, 2013 at 16:28
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    see english.stackexchange.com/questions/4733/…
    – Hellion
    Commented Jun 14, 2013 at 17:11
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    tl;dr for @Hellion's link: If the root is not Latin, use -er. If the root is Latin, use -or. Usually. If you're not British. Probably it's just better to learn them as you go. Commented Jun 14, 2013 at 18:22
  • This is sometimes difficult, even for a native speaker. @KenB, That's great, if you know the origin of all your roots.
    – TecBrat
    Commented Jun 14, 2013 at 19:17
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    @TecBrat For sure. Like I say, it's probably easier to just pick them up as you go. The rule about Latin roots isn't even consistent enough to warrant memorization. Commented Jun 14, 2013 at 19:31

3 Answers 3


As reflected in comments, there's no real "rule" here (though there's a tendency for -or to occur more often in words with Latin roots). So basically, you just have to learn them.

But things aren't as bad as they appear. Not only is the -er form more common in established words - it's far more "productive" for new terms. Also, as RegDwight points out in this ELU answer on the subject, there are many words where either spelling is acceptable (adviser/advisor, convener/convenor, etc.).

So instead of having to learn every word separately, all you have to do is remember those where only -or is acceptable (which as of today, includes administrator).

In short, slow as it might be, the general trend is towards -er. Adopt that as your default, and with any luck by the time you need one of today's more obscure "-or - only" words, the -er form will be acceptable!

EDIT: As @Anixx correctly points out, strictly speaking there is no currently productive suffix -ter in Modern English (the only instances where it's recognized as a meaningful "morphemic element" are laughter::laugh and slaughter::slay). This question and answer address the -or / -er distinction.

  • There is no suffix -ter-, -1
    – Anixx
    Commented Aug 12, 2015 at 10:05
  • @Anixx: I never claimed there was, so a downvote seems a bit harsh. It was simply a misconception on OP's part (which I didn't correct, since it didn't seem central to the question as asked). But per the edit you've prompted me to make, although it's not a productive suffix, there are actually a couple of recognized examples. Commented Aug 12, 2015 at 12:12
  • But in laughter and slaughter you cannot use -tor- anyway and these are not agent nouns. Also what about onslaught? It seems the root could be slaught
    – Anixx
    Commented Aug 12, 2015 at 12:32
  • administrator uses Latin-derived suffix -tor- , not -or
    – Anixx
    Commented Aug 12, 2015 at 12:41
  • @Anixx: Apparently onslaught is only indirectly related to slaughter (through Middle Dutch aenslach). But issues like that are matters of historical linguistics / etymology, which I don't see as central to the needs of nns learners on ELL. The main thing they need to take on board is that -or is both less common and less productive today (and perhaps that any ongoing/future changes in orthography are almost certain to involve switching from -or to -er rather than vice-versa). Commented Aug 12, 2015 at 13:03

There is no suffix -ter- in English.

If the 't' is part of the root, then English uses the suffix -er. If 't' is not a part of the root, then English uses Latin suffix -tor-.

Note that the suffixes have different origin. The suffix -er also was borrowed from Latin but from Latin suffix -ari- (-arius with the ending).

There are also English words with suffix -ster as in hipster, youngster. It was initially a feminine suffix. They should not be confused with the first two.

There are also some words inherited from PIE which had the -ter- suffix in PIE but in English it became a part of the root ("daughter" for instance).


There is also a usage trend to use -tor when the intent is to emphasize that the agent is a person, while -ter is used when the agent is not necessarily a person.

For example, ‘computor’ the original term meaning a person performing computation later becoming ‘computer’ when calculations were performed by either people or machines. Following a transition period where either word was used for either meaning; computer is now commonly understood to mean a machine.

  • Can you give a citation for "computor" being the original spelling? Wiktionary has a non-specific reference for this, but trying to follow it up gets nowhere. Commented Apr 6, 2018 at 4:38
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    Computer was the original spelling; the OED has citations back to 1646 for the -er spelling, and although there are citations for the -or spelling, it doesn't appear that there was ever a systematic distinction between the two spellings in terms of meaning. At all times -er was more common in both meanings. There may have been a trend at some point (perhaps in the mid twentieth century?) but if so, it was certainly not related to how the word was originally spelled, and it seemed to have died out rather quickly.
    – user230
    Commented May 10, 2018 at 21:06

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