A walker or a climber perhaps (7)

I believe the answer is:

rambler

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'a walker' is the definition.
(I know that Rambler is a type of walker)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for rambler that I've seen before include "One who goes on country walks" , "Rover" , "Presumably one goes on" , "Straggling rose" , "Person whose speech is long and disorganised" .)

I've seen this clue in The Globe and Mail.

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