Board a tracked vehicle (7)

I believe the answer is:

entrain

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'board' is the definition.
(entraining is a kind of boarding)

'a tracked vehicle' is the wordplay.
'a tracked' becomes 'en' (I can't justify this - if you can you should believe this answer much more).
'vehicle' becomes 'train'.
'en'+'train'='ENTRAIN'

Can you help me to learn more?

(Other definitions for entrain that I've seen before include "Put on board at the station" , "Get on a rail service" , "Go on board at the station" , "Bring about as consequence" , "Board a rail service" .)

I've seen this clue in The Globe and Mail.

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