In a manner relating to the fourth dimension.

(medicine) The period from the birth of a baby to when the baby is about three months old.

(idiomatic) Full throttle; a maximal level of effort. / Used other than figuratively or idiomatically: see fourth, gear.

Used other than figuratively or idiomatically: see May, fourth.

(Star Wars, fandom slang) Star Wars Day (May 4); the day fans celebrate Star Wars.

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.

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

(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