Crossword Genius

Part of track for the night train? (7)

Ross

I believe the answer is:

sleeper

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

'the night train?' is the definition.
(I've seen this before)

'part of track' is the wordplay.
I cannot quite understand how this works, but
'part' could be 'lee' (lee is a kind of part) and 'lee' is present in the answer.
This explanation may well be incorrect...

'for' is the link.

Can you help me to learn more?

(Other definitions for sleeper that I've seen before include "Kipper" , "Brace to support rail on track" , "Express tears over one" , "Rail supporter; secret agent" , "Railway track support" .)

I've seen this clue in The Telegraph.
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