Mouthwash is a liquid you put in your mouth, move around, and then spit out. People use it to make the breath smell fresh, and some kinds are meant to help with infection or sore places in the mouth and gums. It does not replace a toothbrush; it is an extra step after you brush, or a special liquid a dentist gives you. You do not swallow it on purpose. In a bathroom it often sits next to the toothpaste. The word is almost always a noun in everyday talk.