Come off train (4,3)

I believe the answer is:

work out

I'm a little stuck... Click here to teach me more about this clue!

'train' is the definition.
(thesaurus)

'come off' is the wordplay.
'come' becomes 'work' (I can't justify this - if you can you should give a lot more credence to this answer).
'off' becomes 'out'.
'work'+'out'='WORK-OUT'

Can you help me to learn more?

I've seen this clue in The Independent.

Want a hint initially instead of a full solution? Install my app