Apples, onions, veal or chicken, and pickled herrings, minced fine, and eaten with oil and vinegar; some derive the name of this mess from the French words SELON MON GOUST, because the proportions of the different ingredients are regulated by the palate of the maker; others say it bears the name of the inventor, who was a rich Dutch merchant; but the general and most probable opinion is, that it was invented by the countess of Salmagondi, one of the ladies of Mary de Medicis, wife of King Henry IV. of France, and by her brought into France.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Salesman’s Dog * SalmonNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes