Best officer in uniform one with chum (8)

I believe the answer is:

ultimate

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'best' is the definition.
(I've seen this before)

'officer in uniform one with chum' is the wordplay.
'officer in uniform' becomes 'ult' (I can't justify this - if you can you should give a lot more credence to this answer).
'one' becomes 'I' (Roman numeral).
'with' says to put letters next to each other.
'chum' becomes 'mate' (I've seen this before).
'ult'+'i'+'mate'='ULTIMATE'

Can you help me to learn more?

(Other definitions for ultimate that I've seen before include "The final point" , "Conclusive" , "Furthest, final" , "Eventual" , "Utmost or extreme" .)

I've seen this clue in The Sun.

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