In essence, lineups outrage jailors not involved in dispute (7)

I believe the answer is:

neutral

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'in' is the definition.
Both the definition and answer are adjectives. Maybe they are linked in a way I don't understand?

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

Can you help me to learn more?

(Other definitions for neutral that I've seen before include "Impartial; colour" , "Gear position" , "Impartial; colourless" , "Renault altered" , "uncommitted to either side" .)

I've seen this clue in The Irish Times.

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