One side hearing report of lofty Harry? (10)

I believe the answer is:

hypotenuse

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'one side' is the definition.
(side of a triangle)

I don't understand the remainder of the clue.

(Other definitions for hypotenuse that I've seen before include "long line" , "Right-angled triangle's longest side" , "Long side of right-angled triangle" , "Subject of 1 across's theorem" , "Longest side of right-angled triangle" .)

I've seen this clue in The Guardian.

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