The word greyhound has been around since Old English, albeit with a variety of spellings. At different times, it took the forms grighund, greihund, greahund, grehound, grihond, and grayhound until greyhound took over in the sixteenth century. You may have noticed that the first element of the word didn't really look like the word grey originally; in fact, grey has nothing to do with it. The term was folk etymologized by people who concluded that, because the canines were often grey in color, that had to be the correct spelling. Actually, the word traces to Old Norse grøy, meaning "bitch" (unknown origin), and hund, which was Old English for "hound" (and, through Proto-Germanic hundaz, traces to the Proto-Indo-European root kwo, meaning "dog"). The Greyhound transportation corporation was so named because its founder saw a reflection of a bus in a store window, thought it looked like a greyhound dog, and decided to name his company after that.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.