Crossword Genius

Method of transport making one complain persistently (4)

Ross

I believe the answer is:

rail

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'method of transport' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for rail that I've seen before include "Track - complain - bird" , "method of transport" , "Scold, berate" , "Bar of rolled steel" , "Barrier around lair" .)

I've seen this clue in The Telegraph.
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