Yours, Etc.: Origins and Uses of 8 Sign-Offs
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.