Island, 1/63,360 miles (4)

I believe the answer is:

inch

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'island' is the definition.
(inch can mean a small island)

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

(Other definitions for inch that I've seen before include "Move forward slowly and carefully" , "Edge towards" , "Fraction of a foot" , "Small Scottish island" , "2.54 centimetres" .)

I've seen this clue in The Guardian.

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