Janus was the Roman two-faced god of doors, gates, beginnings, and endings. He gave his name to the first month of the year and to the guy with the fat bunch of keys on his hip: the janitor.
Logophiles – word lovers, but you knew that, didn't you? – have another association with Janus. "Janus words" are those that serve as their own antonyms. "Autoantonym," self-antonym, and "contronym" are other ways to express the same concept.
Some Janus words are just two historically different words that evolved until they both ended up in modern English written the same way. Cleave is Exhibit A for this subcategory of words. Cleave meaning to adhere or to stick (the biblical "a man ... shall cleave unto his wife") derives from the Old English clifian. Cleave meaning to split comes from the old English cleofan.
Eventually people stopped using cleave very often in either sense and opted for "stick" or "split" instead. Smart move.
Sanction is often mentioned on lists of Janus words. It is rooted in the idea of "being made sacred or inviolable." An athletic event may be "sanctioned" by some governing body.
But sanction can also mean the punishment that enforces a law, notionally "making it sacred or inviolable." Used as a verb meaning "to hit with a sanction" and applied to a person, it became a synonym for "punish."
Question isn't a Janus word in the strict sense, but it can cut both ways and cause confusion. As an editor, I sometimes see it used where plain old ask would do the job.
For instance: "He questioned whether they had enough gas for the trip." The inference here is that "they" have been assuming they had enough gas but "he" thinks maybe not. By contrast, "He asked whether they had enough gas" suggests it is an open question: "Do we have enough gas?" "Hmm, dunno. Let's look at the gauge."
Then there is the distinction between "no question of" and "no question but."
"There is no question of his being able to go" means, at a literal level, at least, that "he" won't be able to go.
Thus Reuters quoted Javier Solana, foreign policy chief of the European Union, last month on the EU's policy toward Iran: "For the moment the EU position has not been changed and there is no question of its changing."
We could drive a truck through that "for the moment," but let's not fret about that for now. The "no question but" construction, on the other hand, posits certainty in the other direction.
The Los Angeles Times quoted GOP presidential hopeful Mitt Romney on the campaign trail in Iowa: " 'When it comes to deciding who's going to be the toughest who deals with criminals, there's no question but that my record suggests that giving out no pardons is a heck of a lot better than giving out 1,033 pardons,' Romney told reporters at a trucking-company warehouse in Fort Dodge."
ABC News rendered Romney's quote as "who's gonna be the toughest." That's probably what he said but ABC departed from the print convention of rendering quotes in standard English. It also added a comma: "no question, but that my record suggests..." No question but that somebody at ABC may not be quite up to speed on the idiom.
Of course, when a matter truly is settled, neither of these "no question" idioms gets used at all.
Literally seems to be the Janus word that really sets people off. In a Slate piece a couple of years ago, lexicographer Jesse Sheidlower called it "the word people love to hate." It qualifies as a contronym because it's used both at face value – "the restaurant is literally five minutes' walk from here" and as a metaphor: "He literally blew his top."
Some literalists about literally would argue that what's needed here is "He metaphorically blew his top." But having to say, "I'm using a figure of speech" is right up there with "I was trying to be funny."