The words flammable and inflammable mean the same thing, but (to someone unfamiliar with their meaning) appear to be opposites (because of the "in" prefix). Is there a name for such word pairs that appear to be opposites but actually mean the same thing?

A few other examples are ravel/unravel, regardless/irregardless, radiation/irradiation, incite/excite, culpatory/inculpatory, press/depress, to/unto, part/depart, fat chance/slim chance, thaw/dethaw/unthaw, candescent/ incandescent, canny/uncanny, dead/undead, write up/write down, valuable/invaluable, habitable/inhabitable

  • irregardless is a double negative, having both the prefix ir- and the postfix -less?
    – gerrit
    Oct 12, 2019 at 19:40
  • I'd take issue with some of these. 'Irregardless' per se; 'invaluable' is far more than merely valuable. 'Write up' and 'write down' are not interchangeable to an appreciable degree. Feb 2, 2021 at 14:27

5 Answers 5


How about false enemies?

I originally voted to close because I thought synonym was an adequate generic term here, but Stephen's comment re false friends prompted me to Google language "false enemies". It seems clear that this coinage has occurred to others (here it is in a Wikipedia talk page, for example).

The first other "clear-cut" example I came up with was ravel / unravel, but I've found a couple more since, as have others here - maybe OP's right, we need a word to Know thine enemy!

EDIT: If an out-and-out neologism is acceptable, there's always the crypto- prefix (secret, hidden, or concealed), so they could be cryptosynonyms (though I must admit that one doesn't yet seem to have occurred to anyone else within the scope of Google's indexing routines).

  • 1
    Oddly, ravel seems to have the same property as cleave - it is its own opposite. Feb 21, 2012 at 14:00
  • @Matt: There are actually quite a "autoantonyms" like this. for example, buckle (fasten/collapse), let (allow/hindrance) rent (lend/hire). But not so many where an apparently opposite "inflected form" shares the same meaning as the base word. Feb 21, 2012 at 14:18
  • Great answer, but I'm not sure it quite answers (just because I'm not sure there is an answer). Bounty has been started, but I expect we probably will not get an authoritative answer. Probably what we can expect is support of these suggestions.
    – yoozer8
    Feb 24, 2012 at 2:03
  • How about press and depress?
    – Jim
    Feb 24, 2012 at 4:24
  • @Jim: That's quite a good one! But like the others in the link I put in my comment above, it's only a synonym in certain contexts. I still only see two clear-cut "totally false enemies", and if I'd made my answer "community wiki" so you could edit that one in, I might have been tempted to edit it out as "context-dependent". Feb 24, 2012 at 5:10

According to Wikipedia:

"Flammable and inflammable both mean capable of burning. The word "inflammable" came from Latin inflammāre = "to set fire to," where the prefix "in-" means "in" as in "indoctrinate", rather than "not" as in "invisible" and "ineligible". Nonetheless, "inflammable" is often erroneously thought to mean "non-flammable"."


I don't think there's a name for this -- it's just that the latin prefix "in" can mean either "not" (as "indiscreet") or also literally "in", as in "in-flames"-able.

  • 9
    I used to work with a guy who jokingly used the term 'tuitive' for something that was difficult to use.
    – tinyd
    Feb 6, 2012 at 15:34
  • Note to OP: While I don't think there's a "real" word for the thing you're asking (as fumblefingers pointed out), many comedians might try to work such things into their skits on oxymorons. What you're asking isn't an oxymoron, I'm just saying that some might mistakenly lump these in with other oxymorons.
    – Olie
    Feb 6, 2012 at 21:57
  • 1
    @tinyd: Years ago, every other country pub in the South-West of England had a round tuit on the wall over the bar. They still took ages getting a round ToServingMe, though. Feb 21, 2012 at 14:27
  • @Olie +1 for the prefix/no-name-because-it's-a-coincidence note. I've started a bounty to see if anyone has an actual term for this (although I expect FumbleFingers's answer below is probably the best we will get).
    – yoozer8
    Feb 24, 2012 at 2:04
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    But OP didn't ask for definitions of his first example word-pair, or an explanation of how they came to exist. He asked for a generic name for such pairs - which you have only acknowledged by saying "I don't think there's a name for this". I fail to see this is any answer at all, and I do not understand why so many people have upvoted it. Feb 26, 2012 at 21:27

No, there is no word for describing such pairs. It is because the etymology of both the "in" prefixes are different. The in- in inflammable was derived from the Latin preposition meaning en- (like en-flamed) and not the Latin prefix meaning -un.

  • 6
    Why does it follow from the fact that the etymology of the prefix is not the obvious one that there is no such word for describing such a situation?
    – waiwai933
    Feb 26, 2012 at 2:25

There is a related concept neologistically known as the "contranym" or "antagonym", which is words which mean two opposite things, so for example "to Cleave" can mean "to sever", or "to adhere tightly".

Obviously the concept you're looking for is the precise opposite of this. Can I therefore suggest that by analogy these words ought to be called "homogenyms" (from "homogeneous" meaning "essentially alike")?

(I initially wanted to suggest "homonyms", but that's already taken.)

  • 1
    Just fun trivia: cleaved and cloven are both the past tense of cleave, but they have distinct meanings (the first to join, the second to split).
    – ErikE
    Mar 1, 2012 at 0:59

Well if we're just looking for neologisms I would suggest the obvious:


  • I up-voted for the idea of making it one word, but I think "inantonyms" (along the lines aluded to by other answerers) would be better. Mar 5, 2012 at 7:07

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