To win somethings three times consecutively.(verb)
A third successive win.(noun)
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Use "threepeat" in a sentence
"Pojoaque Valley and Socorro are meeting for a second time, while St. Michael's is looking to add another meaning to the word threepeat against Santa Fe Indian School."
"LOS ANGELES The Los Angeles Lakers celebrated their third consecutive NBA title Friday with a triumphant parade and promises to thousands of fans that the team will top its "threepeat" with a fourth championship next year."
"Any etymologist will tell you "threepeat" isn't a word."