Area around a mouth

DELTA

Think of where a river splits before meeting the sea, forming a triangular shape.

The clue "Area around a mouth" plays on two meanings of "mouth." One is the literal mouth of a person or animal, but the other refers to the mouth of a river—where it meets the sea or a lake. The land formed by sediment at this spot is called a delta, named after the triangular shape of the Greek letter delta. So, the answer cleverly shifts from anatomy to geography.