The word "horse" is a modern name. In classical Latin, the ancients called it "equus." Horses are also known in the animal category as "equine" because of the Latin root word. In common Latin, which we would consider slang, the term for horse was "caballus." This is where we get more common words such as cavalry, caballero (cowboy) or the French word, cheval. Now in the Greek, they used the word "hippo" for horse. What common animal name goes along with "hippo"? The hippopotamus! Hippopotamus is a two part word meaning: horse and river. Potomas means river. So the Greeks named this strange animal that lives in rivers but lightly resembles a horse, a "river-horse".
There are a number of words in this webquest that may be confusing to you. Here are some vocabulary words you can look up and study: