Oust from the position of Detective Inspector (8)

I believe the answer is:

displace

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'oust' is the definition.
(thesaurus)

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

(Other definitions for displace that I've seen before include "Remove from usual habitat" , "Shift" , "Oust" , "Move out of position" , "Succeed" .)

I've seen this clue in the Evening Standard.

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