Is it ensure, insure, or assure?
c.1600, people or things, "mingled confusedly, grouped together without order, consisting of a disorderly mix; indiscriminate," from Latin promiscuus "mixed, indiscriminate, in common, without distinction," from pro- "forward" (see pro-) + miscere "to mix" (see mix (v.)). Meaning "indiscriminate in sexual relations" recorded by 1857, from promiscuity. The Latin adjective was used with conubia (e.g. between patricians and plebeians). Related: Promiscuously.