A yowl is a loud cry or howl, especially one that an animal makes. If you accidentally step on your cat's tail, you'll probably hear her yowl. Poor kitty.
Use this imitative word as a noun or a verb, any time you're describing a wild cry of distress. Your new puppy may yowl all night long the first couple of times you make him sleep in a crate at the foot of your bed — and if his yowling goes on too long, you may find yourself starting to yowl along with him.