It’s a bona fide Latin viral sensation — repeated ad nauseam on CNN and Fox News, in the halls of Congress, and on the president’s Twitter feed. It seems as though the fate of the presidency might hinge these days on three short words of ancient provenance: quid pro quo.

A favorite of classics majors and contracts lawyers, it has clearly befuddled a large segment of the population. Google searches of the phrase have spiked over the last month, and dictionary lookups on Merriam-Webster’s website have surged between 5,000 and 14,000 percent in recent days.

The biggest spike came last Friday. That was the day after acting White House chief of staff Mick Mulvaney appeared to admit that President Trump had engaged in a quid pro quo with Ukraine to further the president’s political interests.

Trump has repeatedly insisted there was “no quid pro quo.’’ Democrats say there was — but even if there wasn’t, he could be impeached. Some linguistic experts just want the phrase to go away.

“I think if I hear it one more time, I’m going to tear my hair out,’’ said Alan Perlman of Rindge, N.H., who has a doctorate in linguistics and often testifies in legal disputes over the meaning of words in prenuptial agreements and other contracts.

Perlman takes the view there was no quid pro quo in the Ukraine affair. “Where is the evidence of one thing exchanged for another?’’ he said. “Not there, apparently.’’

Merriam-Webster, the venerable Springfield-based dictionary company, defines quid pro quo as “something given or received for something else,’’ and says it comes from the New Latin phrase meaning “something for something.’’ Its earliest usage in the English language dates to the 16th century, in apothecaries that substituted one medication for another, sometimes fraudulently.

Over the centuries, it has retained its air of dirty dealings and dark exchanges done on the sly. Think of Anthony Hopkins as Hannibal Lecter in “The Silence of the Lambs’’ cooing to Jodie Foster as FBI agent-in-training Clarice Starling, “Quid pro quo. I tell you things, you tell me things.’’

While the phrase can refer to a neutral exchange, Orin Hargraves, a lexicographer in Colorado, said it’s commonly associated with nefarious words like corruption, harassment, and bribery.

“Words, as a rule, get their reputation by the company they keep,’’ Hargraves said. “So, as soon as you use it, people are thinking more negatively than positively.’’

Quid pro quo, he said, is hard to use neutrally because “what’s completely absent from the phrase is generosity or kindness.’’

That has made quid pro quo the essential catchphrase in the impeachment debate.

In the Democrats’ formulation, Trump allegedly threatened to withhold millions in aid — the quid — until he got Ukraine to agree to investigate former vice president Joe Biden and his son Hunter — the quo.

Asked last month what quid pro quo would look like to him, Senator Lindsey Graham, one of Trump’s staunchest defenders, offered his own unofficial definition, not found in any dictionary.

“ ‘Uh, hey pal, you know, you need to like, go after the Bidens or I ain’t gonna give you any money,’ ’’ he said. “Be really, like, thuggish about it.’’

Democrats have responded that even if Trump’s threat wasn’t perfectly explicit, he could still be impeached.

“An explicit quid pro quo isn’t required to betray your country,’’ Representative Adam Schiff, the House point-man on the impeachment inquiry, tweeted last month.

Richard Thomas, a classics professor at Harvard, noted that quid pro quo has been subjected to competing interpretations advanced by forces on both sides of the impeachment divide.

“It’s a somewhat rarefied phrase,’’ he said. “It sort of attracts attention when the issue behind it is one that is filled with ambiguity.’’

Martin G. Weinberg, a prominent criminal defense attorney in Boston, said that, in the legal context, the phrase means a “corrupt exchange’’ where one person pays or promises to pay another in return for an official act. While “quid pro quo’’ doesn’t appear in the criminal statutes, judges, he said, will often refer to it when giving instructions to a jury assessing whether a politician engaged in bribery.

“It doesn’t need to be explicit,’’ he said. “You can have circumstantial evidence other than express words. Most people engaged in the most common forms of political bribery don’t write a contract and don’t speak in legal terms, but it’s consistent with the context.’’

Mary Kate Cary, who teaches political speechwriting at the University of Virginia, said she’s noticed that pundits who bray about quid pro quo on television never actually define it.

“They say, ‘We know there was quid. Was there a quo?’ ’’ she said. “And they start dissecting the meaning of the phrase without explaining the meaning of the phrase in the first place, and I imagine if you haven’t taken some Latin, that adds to the feeling of elites who are highly educated speaking in ways no one understands.’’

Such esoteric language is more common in the corporate world than in Washington, she said, where politicians try to “speak in plain-spoken ways that people understand and that make them sound authentic and believable.’’

“This is one of those rare phrases in politics that not everybody knows what it means,’’ said Cary, a former speechwriter for President George H. W. Bush.

Perlman, the forensic linguist from New Hampshire, said he sees quid pro quo as the lifeblood of politics, not evidence of an impeachable offense.

“Quid pro quo is baked right into the bone marrow of politics — every political act is a quid pro quo, just about,’’ he said.

Perhaps Trump should just say “mea culpa’’ and move on.

Michael Levenson can be reached at mlevenson@globe.com. Follow him on Twitter @mlevenson.