Uppermost

I think it could be either:

Which length description are you looking for?:

highest

'uppermost' is the definition.
(I've seen this in another clue)

This is the entire clue.

(Other definitions for highest that I've seen before include "Most exalted" , "Above all others" , "Tallest" , "Greatest (number)" , "Most elevated" .)

I've seen this clue in The Mirror.

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