Not the hiker's favourite fruit (5)

I believe the answer is:

acorn

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'fruit' is the definition.
(I know that acorn is a type of fruit)

I can't explain the remainder of the clue.

(Other definitions for acorn that I've seen before include "Fruit-seed of the oak" , "Source of a great oak" , "from which something bigger may develop" , "Potential oak" , "Baby oak?" .)

I've seen this clue in the Evening Standard.

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