AUDIE CORNISH, HOST:

There's a lot of blame being thrown around across Washington this week, and one way to deflect the blame, an expression of metaphorical violence - you know, the one that involves a large vehicle.

(SOUNDBITE OF MONTAGE)

UNIDENTIFIED PERSON #1: That the president threw the United States under the bus...

UNIDENTIFIED PERSON #2: I will throw anyone that gets in front of me under a bus.

UNIDENTIFIED PERSON #3: That was Giants coach Ben McAdoo throwing Eli Manning under the bus.

UNIDENTIFIED PERSON #4: How often do we say that - throw everybody under the bus?

UNIDENTIFIED PERSON #5: I'm not going to throw anybody on my team under the bus.

UNIDENTIFIED PERSON #6: Comey really threw four people or four groups under the bus.

AMMON SHEA: We define throw someone under the bus as to criticize, blame or punish, usually, someone in a vulnerable position, and it's especially in order to avoid blame or to gain an advantage.

ARI SHAPIRO, HOST:

Ammon Shea is an editor at Merriam-Webster. It's a fairly recent addition to our vernacular, he says.

CORNISH: A British politician met this fate in the Financial Times in 1980.

SHEA: And the citation is, some still pin their hopes on the under the bus theory, which has Mr. Foot being forced by ill health to give way to Mr. Healy.

CORNISH: Two years later, it popped up in The Times of London.

SHEA: President Galtieri had pushed her under the bus, which the gossips had said was the only means of her removal.

SHAPIRO: After that, the phrase throw them under the bus crossed to America, where it found a home in sports, business and, most notably, in politics. In 2008, a linguist noted that under the bus appeared in more than 400 stories during that year's presidential campaign.

CORNISH: A lot of throwing, a lot of buses - and Ammon Shea of Webster's believes it's almost always used by a third party discussing other people, never as a direct threat or in reference to oneself.

SHEA: We have very few, if any, examples of somebody saying, I will throw you under the bus.

SHAPIRO: So watch out, vulnerable underlings everywhere.

(SOUNDBITE OF SONG, "THROW 'EM UNDER THE BUS")

NORE: (Rapping) Throw them under the bus. Throw them. Throw them under the bus. Throw them. Throw them. Throw them under the bus.

SHAPIRO: Look both ways before crossing the street, and look behind you, too. Transcript provided by NPR, Copyright NPR.