Crossword Genius

Quells argument when last piece is inserted into medical device (10)

Ross

I believe the answer is:

peacemaker

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'device' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

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

Can you help me to learn more?

(Other definitions for peacemaker that I've seen before include "Reconciler of enemies" , "mediator" , "'Revolver'" , "Eirenic type" , "Person who reconciles enemies" .)

I've seen this clue in The Irish Times.
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