Served in the army? Not one joined (8)

I believe the answer is:

soldered

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

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

(Other definitions for soldered that I've seen before include "Joined metals by melting alloys" , "Joined with metal alloy" , "stuck together" , "Joined metals using soft alloy" .)

I've seen this clue in The Guardian.

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