1.verbTo divert (a locomotive or train) on to a lesser used track in order to allow other trains to pass.
2.verbTo 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.
"I hope you can sidetrack the teacher with questions so we don't have to take the exam."
3.verbTo sideline; to push aside; to divert or distract from, reducing (something) to a secondary or subordinate position.
"He has sidetracked this debate for far too long."
4.verbTo deviate briefly from the topic at hand.
"Just to sidetrack a little bit from the subject I will explain my reasoning."