(rail transport, usually in the plural) One of the two rails of a railway track with which the wheels of a train make contact. / (horse racing) A fence which marks the inside edge of a racecourse.

plural of running rail

plural of running line

present participle of run lines

(rail transport) A railway line used to operate trains on, as opposed to a siding.

(of a locomotive, train, etc.) Its first trip in service, in some cases after a rebuild.

(often followed by of) to risk something important.

plural of running shed

(rail transport) A building used for the maintenance and preparation for service of locomotives.

Subject to strenuous effort or tough competition.