|Origin:||plummet 'metal weight on a plumb line' (14-21 centuries), from Old French plommet 'small ball of lead', from plomb; PLUMB1|
plum‧met also plummet down [intransitive]
to suddenly and quickly decrease in value or amount [= plunge]
plummet from something to something
Profits plummeted from £49 million to £11 million.
House prices have plummeted down.
to fall suddenly and quickly from a very high place [= plunge]:
The plane plummeted towards the earth.