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
  1. noun
    a line enclosing a plane area
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    type of:
    a length (straight or curved) without breadth or thickness; the trace of a moving point
  2. noun
    the boundary line or the area immediately inside the boundary
    synonyms: border, margin
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    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
  3. noun
    the size of something as given by the distance around it
    synonyms: circumference
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    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)
Commonly confused words

parameter / perimeter

Parameter is a limit that affects how something can be done, and perimeter is the outline of a physical area. Both words have special meanings in math, but they take off their pocket protectors and relax their definitions when they join the rest of us.

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