hamburgeryoudaoicibaDictYouDict[hamburger 词源字典]
hamburger: [19] As its inherent beefiness amply demonstrates, the hamburger has nothing to do with ham. It originated in the German city and port of Hamburg. The fashioning of conveniently sized patties was a common way of dealing with minced beef in northern Europe and the Baltic in the 19th century, and it appears that German sailors or emigrants took the delicacy across the Atlantic with them to America.

There it was called a Hamburg steak or, using the German adjectival form, a Hamburger steak. That term is first recorded in the late 1880s, and by the first decade of the 20th century the steak had been dropped. By the 1930s the hamburger had become an American fast-food staple, and products similar in concept but with different ingredients inspired variations on its name: beefburger, cheeseburger, steakburger, and so on; and by the end of the decade plain burger was well established in the language.
[hamburger etymology, hamburger origin, 英语词源]
hot dogyoudaoicibaDictYouDict
hot dog: [19] This term for a cooked sausage or frankfurter in a bun has its origins in the mid- 19th-century use of dog as an American slang term for a sausage (perhaps an allusion to the sausage’s often dubious contents). By the 1890s hot dog was Yale University slang for a cooked sausage bought at a fast-food stall, and by 1900 it was in widespread use for the whole deal, bun and all. Since then it has never looked back. (The widely repeated story that the term was invented by the US cartoonist ‘Tad’ Dorgan in the early 1900s is quite untrue.)
pizzayoudaoicibaDictYouDict
pizza: [20] Italian pizza is quite a broad term, signifying ‘cake’, ‘tart’ or ‘pie’ and encompassing dishes as diverse as a closed fruit pie and a flat bread-dough base with a topping. It is the latter, of course, that brought the word into English. At first, both the word and the foodstuff were unfamiliar enough for the tautologous name ‘pizza pie’ to be deemed necessary, but the fast-food revolution from the 1960s onwards has thoroughly naturalized pizza (US fast-food outlets have their own abbreviation, za).

The origin of the Italian word is uncertain. It has been linked with Vulgar Latin *picea, a derivative of Latin pyx ‘pitch’ (in which case it would be paralleled by Welsh bara pyglyd, literally ‘pitchy bread’, possibly a reference to its colour, from which English gets pikelet [18], the name of a type of tea-cake), but it could also be related to modern Greek pitta (source of English pitta [20]), which may be a descendant of classical Greek peptos ‘cooked’.