LONDON — Britain’s withdrawal from the European Union, known as Brexit, has brought a multitude of challenges, and now it seems to be testing the limits of the English language. Clever wording, what diplomats describe as constructive ambiguity, can bridge gaps between groups with competing interests. But lately, the language in Brexit seems only to have set off seismic shocks.

On Monday, it was the use of the innocuous-sounding word “alignment” that crashed hopes of a breakthrough in Brexit talks, prompting a political crisis in London and sending diplomats scurrying to their dictionaries in search of alternative terminology.

If parsing the language has proved difficult for diplomats, average readers have often found themselves sinking in a swamp of seemingly meaningless distinctions and incomprehensible verbiage.

Herewith, a guide to the language that brought Brexit to a halt this week and what it may take to put talks with the European Union back on track.

The current linguistic troubles are being generated by the logjam over the border between Northern Ireland, which is part of the United Kingdom, and Ireland, which will remain in the European Union. Prime Minister Theresa May of Britain is under pressure to guarantee that, after Brexit, there will be no border checks between the two. This is harder than it sounds.

Currently, as both sides are members of the European Union, trade flows over the border unimpeded, thanks to their membership in the single market and customs union. But after Brexit, this presumably will no longer hold, since Britain has pledged to leave the single market and customs union, and set up its own rules and standards. But no one wants the “hard border” that existed until it was dismantled as part of the peace process that ended the sectarian fighting in the late 1990s.

So the question becomes how to thread the needle. How can trade keep flowing freely — which requires that the European Union and United Kingdom have pretty much the same rules and standards — after Brexit, when the point of leaving is for the United Kingdom to establish rules and standards independently of the European Union?

On Monday, Mrs. May thought she had the answer. The reliable Irish broadcaster, RTE, reported that in the draft text of an agreement that was shared with Dublin, Britain would guarantee that there would be “no regulatory divergence” on key issues on the island of Ireland. That suggested signing up to many of the same rules and standards as the European Union, in this way eliminating the need for customs checks on the Irish border, keeping many things pretty much as they are now.

If Mrs. May thought that was problem solved, she soon learned better. To Northern Ireland unionists, who dread any hint of unity with the south, any scheme that treats them as separate from the rest of the United Kingdom is their worst nightmare. To them, Plan A sounded like a pit stop on the road to a united Ireland.

All good diplomats have a fallback plan, in this case replacing the phrase “no regulatory divergence” in the draft text with “continued regulatory alignment.”

How this change was supposed to solve the problem was not explained, as it means more or less the same thing. In any event, it was probably too late. Arlene Foster, leader of the Democratic Unionist Party, a small Northern Irish party which is propping up Mrs. May’s government in Parliament, said she opposed anything that “separates Northern Ireland economically, or politically, from the rest of the U.K.”

At this point, Scotland’s First Minister, Nicola Sturgeon, and the mayor of London, Sadiq Khan, both of whom strongly oppose Brexit, piped up to say that if Northern Ireland could have a separate deal from the United Kingdom, then so should they.

Mrs. May, at a lunch in Brussels on Monday where she had expected to clinch a deal on Britain’s divorce, setting the stage for the next phase of talks on trade, suddenly rushed from the table to call Ms. Foster. Minutes later, she was forced to admit that the whole deal was temporarily off.

On Tuesday it was left to the Brexit secretary, David Davis, to find a way out of the linguistic dead end. “The presumption of the discussion was that everything we talked about applied to the whole United Kingdom.” he said. “I reiterate that alignment isn’t harmonization. It isn’t having exactly the same rules. It is sometimes having mutually recognized rules, mutually recognized inspection — that is what we are aiming at.”

This explanation was designed to reassure the unionists that “regulatory alignment” would affect the whole of the country — not just Northern Ireland.

Loosely translated, this meant signing up to some European Union standards, but reaching them through a parallel British system that achieved the same outcome. Whatever that was, it would apply to the entire United Kingdom, not just Northern Ireland.

If that calmed some nerves in Belfast, however, it set off new alarms in London among hard-line supporters of Brexit. They want a clean break with Brussels, so to them any hint that the country might sign up to a set of European Union rules, by any means, is anathema.

On Wednesday, the pro-Brexit Conservative Party lawmaker, Jacob Rees-Mogg, used characteristically polite, if colorful, language to accuse Mrs. May of backsliding on the red lines she laid down in Brexit negotiations. Mr. Rees-Mogg appealed to Mrs. May to apply “a new coat of paint to her red lines,” adding that “on Monday they were beginning to look a little bit pink.”

That remains to be seen. But one possible avenue is a mechanism established under Strand 2 of the Good Friday Agreement, which ended decades of violence, and subsequent accords. These delineates areas — energy, agriculture, food safety and transport, among them — where the two sides can make special rules that apply only to Ireland, north and south. Perhaps, they can build on these and agree on a plan for “mutually recognized rules” along the lines of what they already have.