third rail

American  

[thurd reyl] / ˈθɜrd ˈreɪl /

noun

1. Railroads.

   1. a rail laid parallel and adjacent to the running rails of an electrified railroad to provide electric current to the motors of a car or locomotive through contact shoes.

   2. an additional running rail laid on the same ties as the two regular rails of a railroad track to provide a multigauge capability.

2. a controversial topic or issue in the public sphere that people, especially politicians, try to avoid discussing (often used attributively): Doping is the third rail of the Olympics.

   a third-rail subject;

   Doping is the third rail of the Olympics.

   Social Security is the third rail of American politics.

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third rail British  

noun

1. an extra rail from which an electric train picks up current by means of a sliding collector to feed power to its motors

2. politics

   1. a cause or topic that is considered extremely dangerous for a person to support or comment on

   2. ( as modifier )

      a third-rail issue

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third rail Idioms  

1. Something that is dangerous to tamper with, as in Anything concerning veterans is a political third rail. This term alludes to the rail that supplies the high voltage powering an electric train, so called since 1918. On the other hand, grab hold of the third rail means “become energized.” Both shifts from the original meaning date from the late 1900s.

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Etymology

Origin of third rail

An Americanism dating back to 1865–70

Example Sentences

His work involves what some view as the third rail of journalism: AI playing a leading role not just in researching, but in writing stories.

From The Wall Street Journal • Mar. 27, 2026

Lehotsky argued plainly that “It’s the constitutional third rail, or it should be, for the government to insist it can engage in viewpoint discrimination.”

From Salon • Jul. 28, 2025

“You can touch this mythical third rail and live to see another day.”

From Los Angeles Times • Jul. 1, 2025

In Iowa, however, attacking the mandate has been a third rail of politics.

From Washington Times • Jul. 7, 2023

“Don’t you know about the third rail? Fry you up.”

From "Clayton Byrd Goes Underground" by Rita Williams-Garcia