Simple past tense and past participle of plunge.(verb)
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Use "plunged" in a sentence
"His approval among Republicans has plunged from a weak 41% to sickly 30% What's more, 58% of middle-class voters approve of him vs. 69% last month."
"Thanksgiving dinner; but before she could broach the subject Martin plunged into the one with which he was full."
"Keon Blake went back into surgery Tuesday, the latest in what his mother says will be a series of operations to repair broken facial bones and two broken femurs suffered when the 17-year-old senior plunged from a third-floor balcony above the atrium of McKinley Technology High School Friday evening."