Cycle round French city alone (4)

I believe the answer is:

only

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'alone' is the definition.
(I know that alone can be written as only)

I don't understand the remainder of the clue.

(Other definitions for only that I've seen before include "Except that; single" , "Merely; single" , "Unique; merely" , "Solely; except that" , "Mere" .)

I've seen this clue in The Guardian.

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