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1873, "set of five things" (originally in music), from quintuple (adj.) with ending from triplet. In plural, "five children at one birth" it is recorded from 1889.
quintuplet quin·tu·plet (kwĭn-tŭp'lĭt, -tōō'plĭt, -tyōō'-, kwĭn'tə-plĭt)n.
One of five offspring born in a single birth.
A group or combination of five associated by common properties or behavior.