plural of fourth rail

(rail transport) 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.

(US, slang, originally and chiefly military) Ass (buttocks or anus).

A hamlet in Sutherland, Highland council area, Scotland (OS grid ref NH8094).

(Christianity, Quakerism) Wednesday (the fourth day of the Judeo-Christian seven day week)

Alternative form of fourche (“forked”)

(obsolete, now historical) The former name of the city of Oriska, North Dakota, used throughout the short period of 1872 to 1881.

plural of fourth grader

(US, education) A pupil who is in fourth grade.

(mathematics) A field of study concerned with the representation or approximation of general functions, such as arbitrary waveforms, by sums of trigonometric functions.