The act of agreeing or arranging together; coordination or a state of being concerted (archaic).
From 'concerted' (from 'concert') plus the suffix '-ment' meaning a state, condition, or action. Rare and somewhat archaic usage.
This word is almost extinct—it was used during the age of diplomacy to describe when kingdoms reached 'concertment' (agreement), but now we just say 'concert of action'!
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