I've been bothered for quite some time by the word sanction, used in the media to describe one country limiting what interaction there is with another, but the same media use the word to indicate an approval for an action. So, when talking about limiting what sued to be ordinary business between Europe and Russia there are sanctions discussed, and then these sanctions are sanctioned. How very confusing.
Words like these, I guessed, must be called contranyms, possibly contronyms (to be consistent with synonym) and probably also called Janus words. To my surprise, I am quite right and that is indeed what others call these words. So a pic of Janus has to be the image for this page. The preferred word is, apparently, contronyms.
A word I don't use is cleave. I now understand why. I know that a tree can be cleaved by lightning just as I know that people might cleave to principles. So simultaneously the word means to stick to something and to divide in twain.
Apology is something you make when things have gone wrong and, in theory at least, you admit responsibility. Too many apologies are made, "sorry", where there is not blame to attach. But it also means a very poor example of something. So I might refer to one of Boris Johnson's many public apologies as being an apology of an apology. A meaning I see in the dictionary but don't use myself is that an apology is also a formal explanation or defence of a belief or system, especially one that is unpopular. So a political apology could be a defence and contrition. Perhaps that means that when a reporter asks a question that cannot be answered for reasons of state, the correct response from the politician is to say they are sorry they cannot answer.
Adumbrate ought to go earlier but I didn't think of it; the two meanings are to disclose and to obscure. No wonder then that we don't use the word in common speech.
Being no plantsman, I've often wondered at what people mean calling a plant an annual, when it doesn't repeat at all. I'm told that would, in the gardening world, be called a perennial, a plant that flowers annually.
I found aught to mean both anything and nothing. I feel we should use naught for the nothing version. "What ho, my man, d'ye know aught of this fellow?", My lord, I know (n)aught". But then one ought to know aught – and of nought, naught. Still with numbers, words we understandably don't use much in maths is enumerate and innumerate. One can enumerate the integers below a thousand but the irrationals between just two and three are innumerable.At least we use disnumerate for a person who can't, though there are dictionaries that give innumerate as an antonym of numerate. Thus one could enumerate the innumerate in a bottom set class - and no doubt no-one would understand; this is the definition of a teacher joke. But then this is a different can of worms, homophonic contronyms.
One can dust a cake with sugar, adding material; one uses a feather duster to remove dust
Fast is a word with many meanings, but two of them describe (i) having your foot stuck fast in mud and so immovable or (ii) being fast with your footwork in a dance move, quite the opposite of the previous state.
Fulsome praise is an expression used, but could mean both copious praise and, remarkably, insincere praise. Not then a phrase to use carelessly. In the same way, fearsome can mean full of fear and causing fear.
Go is another such; we usually use the verb to indicate movement, but it also is used to indicate death ("My phone is beginning to go, oh no it's gone") which might once have meant movement (in a hell/heaven direction) but currently means rather the reverse, immobility. Left works the same way; there were four left in the room at the time I left the meeting. Both movement and immobility indicated in the one word.
Hack, a word much used on the internet, could be a clever, even ingenious trick to get something done but the word also means a temporary fix, probably not at all pretty or even clever, as in th hack about.
A handicap is a loss of ability, a disability. Its use in a sporting context is meant the same, that one is given a disadvantage to even up the field but, the way we use that term has become to mean the opposite, in that one is given a handicap because of excess ability, thus handicap equates with ability, not its lack. I think this classes as somethign different from a contronym, because of a usage habit within our society that takes a word and reverses its meaning for reasons of irony or humour. I might well put cool, sick, hellacious, like hell, the hoi polloi, to take care of, terrific, wicked in the same bracket. I might add lease (both rent and borrow) to the handicap-like list.
One can impregnate something, which is then shown to be impregnable. But a chastity belt is supposed to render the wearer the opposite, impregnable.
A genuinely confusing word is inflammable both able to be flamed and not. What a useless word,
Off when applied to things like alarms is very confusing. The security alarm went off so I went and turned it off. In this case the alarm going off tells you not at all whether it is making noise or not.
Oversight, another word I don't use much, means to provide supervision and simultaneously to miss something. One might apologise for the oversight in your report but it points, in apology, to a failure of the oversight.
If something is priceless, does it have value or not?
If one was a qualified expert, woudl that mean that the expert was limited, as in being also a qualified success?
A quantum leap in physics is a very small change, but in informal English it means a radical change.
Reflexive is generally used as in a reflexive action, which is an automatic, unthinking response. But at the same time it ought to mean something resulting from reflection. I think here we have a word whose meaning is moving and I think we'd use the word reflective for the latter case.
We screen people for possible diseases and we often in hospital screen people off from one another for reasons of privacy, but we screen pictures which is the opposite of privacy. So cctv might be used to screen things that others would prefer to be screened. Oh my, English is a silly language.
Among many words used as slang we choose an opposite meaning, one of these is to use sick to indicate that something is really good (cool, for older folk). Others, dare I say the majority, would see sick as meaning not well, somehow dysfunctional. I'll perhaps add other words forming a group in here.
We use trip to mean both moving and failing to move. We can gaily trip along a pavement until such time as we trip up.
I often wanted to write 'trying' in school reports. I often did, in ways such that while the sentence said one thing, the message was, somehow, the other.
If you have been unbending on an issue, can one then unbend on that same issue? How very silly. The latter is a bad use of language and I don't see how that can be either irony or amusing.
Borrowing the example used in wiktionary, Brtain fought with the USA in one way in 1812 but in another in 1942.
To have a fight with another suggests that this is a contest specifically restricted to two participants as occurs in sport. War is not a sport. The UK also fought with Russia in different meanings in 1812 and 1942. One would usually fight with a weapon, which does not normally mean that the weapon fights back. Those seeking clarity would instead use fight against to show adversaries.
It strikes me that some of these words, but not all, have begun, like dust, as a noun and then become a verb describing some action with the noun. I wonder if (further) research is in order?
Homophonic contronyms:
Cease/seize; raise/raze; petalless, petalous; oral, aural; prescribe, proscribe. I say OWral for the heard one; I say prEscribe and prOscribe. I loved the idea of Gilgamesh razing a city to the ground so he could raise another upon the very same site. I place awful here because the original meaning is now spelled as aweful. The term 'shock and awe' when applied to the Iraq war showed how awful modern weapons can be; to some, this was simultaneously aweful.
Homographic contranyms:
Resign and re-sign can be made to look the same with opposite meanings. I see the sense in the hyphen when one signs a second time. Presumably originally one re-signed a contract as part of the cessation of that contract, hence resigning came to mean the end of a posting. Perhaps, before writing was a general skill and one's own mark was recognised as such, one marked something as started (and marked by the responsible person) and then marked it again as completed, responsibility over. If you were to think in book-keeping terms, a balancing action would cancel the action.
I'm reminded of just this morning coming up with the distinction between a train-worker and a chemist; ask him to pronounce the word unionisation.
[1] https://www.dailywritingtips.com/75-contronyms-words-with-contradictory-meanings/
[2] https://en.wiktionary.org/wiki/Appendix:English_contranyms