Simple past tense and past participle of plummet.(verb)
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Use "plummeted" in a sentence
"They recall, for example, how the value of the Halston label plummeted in the early 1980s after the designer tried to sell his fashions through JCPenney."
"Lamps dismounted from their tables at the slightest touch; pictures plummeted from the wall, the glass in their frames shattering, whenever anyone walked past them."
"If we had just waited, listened calmly while strange shaped ships plummeted from the sky spewing garbled language of conquest."