preservative (adj.)

late 14c., preservatif, "tending to keep safe, sound, or free from harm," from Old French preservatif and directly from Medieval Latin praeservativus, from stem of Late Latin praeservare "guard beforehand" (see preserve (v.)).

The noun is from early 15c., "a preservative medication; substance that preserves corpses," also generally "anything that preserves or maintains." The  sense of "chemical added to foods to keep them from rotting" is from 1875.