Crossword Genius

Traveller's one-liner? (8)

Ross

I believe the answer is:

monorail

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'traveller's one-liner?' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

This is the entire clue.

Can you help me to learn more?

(Other definitions for monorail that I've seen before include "Suspended railway" , "Hanging transport system" , "Type of railway" , "Form of transport" , "train" .)

I've seen this clue in The Telegraph.
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