This book began with two questions. The first came from Katie, the very observant seven-year-old daughter of my old friends Jim and Linda. Katie asked why the label of a ketchup bottle read “tomato ketchup.” (Go look: most of them do.) Isn’t that redundant, she asked? It was a sensible question. After all, if I go into a bar and order a margarita, I don’t order a “tequila margarita.” A margarita is made of tequila. (Otherwise it would be a daiquiri. Or a gimlet. Or even, God forbid, a cosmopolitan.) The tequila is understood.
So why do we mention the tomatoes in ketchup?
—Dan Jurafsky, The Language of Food: A Linguist Reads the Menu