Crossword Genius

Person in authority that must be straight! (5)

Ross

I believe the answer is:

ruler

This clue is a double definition.

'person in authority' is the first definition.
(someone who rules or governs)

'that must be straight' is the second definition.
(a ruler for measuring things must be straight)

(Other definitions for ruler that I've seen before include "Measuring device" , "liner?" , "Drawing stick or monarch" , "Controller" , "Chief" .)

I've seen this clue in The Times.
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