fourth rail

Fetched 2026-10-26 (cache).

Synonyms: fourth wall, fourth rate

Antonyms: fourth wall, fourth rate

Related words from Datamuse; suggestions, not definitions.

Noun

1. {{lb|en|rail}} An extra rail in addition to the {{l|en|third rail}} ([[live rail]]) which is used for [[current]] [[return]] purposes, mainly by [[London Underground]], because of problems caused by using the [[running rail]]s for current return underground.

Source: Wiktionary · CC BY-SA 4.0 (Wiktionary dump) · cached copy, not a rewrite.