Yours, Etc.: Origins and Uses of 8 Sign-Offs
1560s, from French quintuple (15c.), from Late Latin quintuplex, from Latin quintus "fifth" (related to quinque "five;" see quinque-) on model of quadruple. Related: Quintuplicate.
1630s, from quintuple (adj.) or from French quintupler (v.). Related: Quintupled; quintupling.