1670s, "dish of chopped meat, anchovies, eggs, onions, with oil and condiments," from French salmigondis (16c.), originally "seasoned salt meats" (compare French salmis "salted meats"), from salmigondin (16c.), a word of uncertain origin.
Watkins derives it from Latin sal "salt" (from PIE root *sal- "salt") + condire "to season, flavor" (see condiment). The French word is probably related to or influenced by Old French salemine "hodgepodge of meats or fish cooked in wine," which was borrowed in Middle English as salomene (early 14c.). French salmi, meanwhile, made its way into English by 1759 for a particular kind of ragout; Century Dictionary describes it as "A ragout of roasted woodcocks, larks, thrushes, or other species of game, minced and stewed with wine, little pieces of bread, and other ingredients to stimulate the appetite."
Salmagundi in the figurative sense of "mixture of various ingredients" is from 1761; it was the title of Washington Irving's satirical publication (1807-08). In dialect, salmon-gundy, solomon-gundy.