Word.ws English Dictionary

fourth rail

fourth rail noun: an extra rail in addition to the third rail (live rail) which is used for current return purposes, mainly by London Underground, because of problems caused by using the running rails for current return underground.

Noun

fourth rail (plural fourth rails)

  1. An extra rail in addition to the third rail (live rail) which is used for current return purposes, mainly by London Underground, because of problems caused by using the running rails for current return underground.
    • It was the only line to operate by means of the third-rail system (as distinct from the fourth-rail system now universal on all London's Underground railways) and its coaches were of different design and appearance from those on other systems.1948 January and February, C. R. L. Coles, “The Grouping Era”, in Railway Magazine, page 21
    • The railway used the 'Third Rail' system of electrification, like all the early Tubes. (But it would soon be replaced across the network by another system even more exciting - Fourth Rail!)2012, Andrew Martin, Underground Overground: A passenger's history of the Tube, Profile Books, →ISBN, page 103

Forms of fourth rail

pluralfourth rails

Questions about fourth rail

What does fourth rail mean?
Fourth rail means an extra rail in addition to the third rail (live rail) which is used for current return purposes, mainly by London Underground, because of problems caused by using the running rails for current return underground.
What part of speech is fourth rail?
Fourth rail is a noun.
What is the plural of fourth rail?
The plural of fourth rail is fourth rails.

Words near fourth rail in the dictionary

  1. fourth part
  2. fourth person
  3. fourth point of contact
  4. fourth points of contact
  5. fourth position
  6. fourth rail
  7. fourth rails
  8. fourth rate
  9. fourth rates
  10. Fourth Reich
  11. Fourth Republic

Source and license

Adapted from Wiktionary: fourth rail (page history and authors). Text available under the Creative Commons Attribution-ShareAlike 4.0 license. Word.ws reformatted the entry and added links. Wiktionary data of 2026-09-02.

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