The noun perimeter refers to the border of an enclosed space. The perimeter of a house is its property line. For a country, it would be that country’s borders.

From Latin, meaning “around” (peri)and “measure” (metron), a perimeter is basically a boundary of any kind, measuring around the shape. In mathematics, perimeter refers to the length of this boundary. In geometry class, you might be asked to calculate the perimeter of a polygon, which is the sum of the length of each side. You might also hear this word used by members of the military or a police force as in “secure the perimeter” or “the perimeter has been breached.” A basketball player that likes to shoot from the three point line is said to “operate on the perimeter.”

Definitions of perimeter

n a line enclosing a plane area

Type of:
a length (straight or curved) without breadth or thickness; the trace of a moving point

n the boundary line or the area immediately inside the boundary

border, margin
either the outer margin or the inner margin of the aperture of a gastropod's shell
Type of:
bound, boundary, edge
a line determining the limits of an area

n the size of something as given by the distance around it

the distance around a person's body
the expansion of a person's girth (especially at middle age)
Type of:
the physical magnitude of something (how big it is)

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