Fell or dropped very quickly and steeply, often describing a sudden loss or decline.
From Old French 'plomb' (lead weight), via 'plummet' (a lead weight used by surveyors to check if something is vertical). The verb emerged because the plumb weight drops straight down with great speed.
A plumb weight is why we have words like 'plumber'—and 'plummeted' preserves the memory of ancient tools in its dramatic dive, showing how work equipment becomes poetry.
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