Definitions from Wiktionary ( )

▸ noun:  (rail transport) A second, relatively short length of track just to the side of a railroad track, joined to the main track by switches at one or both ends, used either for unloading freight, or to allow two trains on a same track to meet (opposite directions) or pass (same direction); a railroad siding.
▸ noun:  (sometimes) Any auxiliary railroad track, as differentiated from a siding, that runs adjacent to the main track.
▸ noun:  (mining) A smaller tunnel or well drilled as an auxiliary off a main tunnel or well.
▸ noun:  An alternate train of thought, issue, topic, or activity, that is a deviation or distraction from the topic at hand or central activity, and secondary or subordinate in importance or effectiveness.
▸ verb:  (rail transport) To divert (a locomotive or train) on to a lesser used track in order to allow other trains to pass.
▸ verb:  To divert or distract (someone) from a main issue or course of action with an alternate or less relevant topic or activity; or, to use deliberate trickery or sly wordplay when talking to (a person) in order to avoid discussion of a subject.
▸ verb:  To sideline; to push aside; to divert or distract from, reducing (something) to a secondary or subordinate position.
▸ verb:  (intransitive) To deviate briefly from the topic at hand.

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