There is a class of transformations in physics called "orthochronous", meaning that they preserve the direction of time's flow. ("Ortho-" from the Greek for 'straight' or 'right'?) As far as I am aware, while there is no word for the opposite---a transformation that reverses time's flow---there is certainly such a concept. So I need the word to describe that concept, and I can easily think of two possibilities. But I am unclear about the distinctions between them.

  • Heterochronous. ("Hetero-" from the Greek for 'other'?)
  • Parachronous. ("Para-" from the Greek for 'amiss', 'irregular', or 'distinct from'?)

I would lean toward hetero-, but I'm not entirely sure why. My attempts at establishing the Greek origins are amateurish and tentative, of course.

Is there a strong distinction between these two options? If so, which best describes my desired usage; if not, should I just pick one at random?

(I'm also entirely open to better options.)

  • 2
    If you are willing to mix Latin and Greek, perhaps retrochronous?
    – bib
    Aug 21, 2014 at 17:42
  • 1
    How about merlinchronous?? ;-)
    – Jim
    Aug 21, 2014 at 18:21
  • Well, if "ortho" means "right" there's always "sinister". (But seriously, when speaking about time I'd think "retro" would work.)
    – Hot Licks
    Aug 22, 2014 at 1:15

3 Answers 3


The Greek prefix "ortho-" means "right" (in the sense of "correct", ultimately deriving from "straight"), so strictly speaking the antonym should have a Greek prefix meaning "wrong", but neither "dyschronous" nor "cacochronus" quite works.

So perhaps instead of the antonym of "wrong", we could use the antonym of "straight", i.e. "bent" or "crooked", for which the closest Greek prefix is "scoli-", rendering "scolichronous".¹

But I don't particularly like that, either: something moving against the flow of time isn't following a crooked path, nor even a wrong path, it's simply backwards, as in swimming upriver (which is neither wrong nor crooked).

So perhaps we'd like a prefix which means "against" or "backwards". The Greek prefix "ana-" means "against", so one option is "anachronous" (and the related English word "anachronism" does indeed mean "chronologically misplaced", especially something from the past that doesn't belong here in the present; it is against time).

Another option, which I prefer, is "retrochronous"; the drawback is "retro" is a Latin root, but that's outweighed, in my opinion, by the benefits: "retro-" is both more consonant with "ortho-" (ending with o) and more immediately accessible (few know what "ana-" means, but everyone knows what "retro-" means).

¹ I also considered "scalen-" (meaning "uneven", as in "scalene triangle"), for "scalenochronous", but that's a mouthful and no real improvement over "scolichronous", and "presbychronous" for "old time", but that lacks a sense of motion.

  • 5
    Ana- doesn't really mean ‘wrong’ as such (that's more like dys-, though that's really closer to ‘bad’); it just means ‘against’ or ‘back’. In that sense, anachronous is a good antonym to orthochronous. It's easily confused with anachronisms, though, which are a different thing. Aug 21, 2014 at 17:53
  • I like the feel of "ana-", certainly, but I do share Janus's reservation about confusion with anachronism. Any thoughts about "hetero-" or "para-"?
    – Mike
    Aug 21, 2014 at 18:11
  • "Hetero-" means "mixed", so that would work if you had a mixed bag of tachyons, luxons and bradyons, but that's not the situation here. Similarly, "para-" means "beside", so that would work for something outside of time, or progressing along a separate or parallel timeline, as in a multiple worlds ("Sliders") scenario.
    – Dan Bron
    Aug 21, 2014 at 18:13
  • 1
    Oops, it looks like "hetero" means "different (from usual)", not "mixed". That's improves its suitability, relatively speaking, but to me still doesn't seem specific enough: heterochronous might mean "accelerated time", or "decelerated time", or "out of chronological order", or "choppy time", or anything else that's not "plain old time". With that said, it is preferable to other options, for ending in an "o", as "ortho" does.
    – Dan Bron
    Aug 21, 2014 at 18:31
  • I quite like dyschronous. I think it's a reasonable fit. Aug 21, 2014 at 22:54

anti-chronus sounds better to me, b.c anti- has the sense of against


You could try cacochronous, where the greek root caca- or caco- means

bad, harsh, wrong, evil; incorrect; unpleasant; poor; used most of the time as a prefix

There are several example words at the link that use this prefix.

  • Funny, I added to this answer at the same time you did.
    – Dan Bron
    Aug 21, 2014 at 17:59
  • @DanBron - yeah, I hate when that happens. Aug 21, 2014 at 18:02
  • I would suggest using the k though to indicate the Greek origin. The c is decidedly non-Greek.
    – oerkelens
    Aug 21, 2014 at 18:07
  • My concern is that there should be no value judgement -- neither direction can be specified as good/bad, right/wrong. (Maybe orthochronous is imperfectly formed, but we're stuck with it...)
    – Mike
    Aug 21, 2014 at 18:09
  • @oerkelens It's calligraphy and cacophony, though, so using a k would actually probably be more confusing than anything. Aug 21, 2014 at 19:52

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