Authorise Emerson's superiors to detain POW (7)

I believe the answer is:

empower

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'authorise' is the definition.
(I know that authorise can be written as empower)

'emerson's superiors to detain pow' is the wordplay.
'emerson's superiors' becomes 'emer' (I can't explain this - if you can you should give a lot more credence to this answer).
'to detain' indicates putting letters inside (inserted letters are held or detained).
'emer' placed around 'pow' is 'EMPOWER'.

Can you help me to learn more?

(Other definitions for empower that I've seen before include "Entitle" , "Permit" , "Give authority to, authorise" , "Delegate" , "Give authority to, enable" .)

I've seen this clue in the Sydney Morning Herald.

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