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Commercial carrier of swine on a train (6)

Ross

I believe the answer is:

aboard

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'on a train' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for aboard that I've seen before include "Embarked on (a ship)" , "on a yacht maybe" , "Alongside" , "On (eg, a ship)" , "on base" .)

I've seen this clue in the Sydney Morning Herald.
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