Mouth is a noun referring to the opening in the face used for speaking, eating, and breathing.
The term "mouth" can also mean:
1. The opening or entrance of something (e.g. the mouth of a cave)
2. The point where a river flows into a larger body of water
3. In slang, to talk excessively or boastfully ("Don't mouth off to me!")
4. In music, the opening of a wind instrument