Crossword Genius

Captive in luminary, Aristotle, say? (9)

Ross

I believe the answer is:

shipowner

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'aristotle say?' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

'captive in luminary' is the wordplay.
'captive' becomes 'POW' (prisoner of war).
'in' means one lot of letters goes inside another.
'luminary' becomes 'shiner' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'pow' inserted into 'shiner' is 'SHIPOWNER'.

Can you help me to learn more?

(Other definitions for shipowner that I've seen before include "Crafty proprietor" , "I've secured brig" , "man over the line" , "Onassis, say" .)

I've seen this clue in The Times.
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