Entry from British & World English dictionary
noun British informal
1 (also sweet Fanny Adams) Nothing at all: I know sweet Fanny Adams about mining 2A nautical term for tinned meat or stew.
late 19th century (in sense 2): black humour, from the name of a murder victim circa1870. sense 1 dates from the early 20th century, and is sometimes understood as a euphemism for fuck all.
Definition of Fanny Adams in: