perimeter (n.)

early 15c., perimetre, "circumference, outer boundary, or border of a figure or surface," from Latin perimetros, from Greek perimetron "circumference," from peri "around, about" (see peri-) + metron "measure" (from PIE root *me- (2) "to measure"). Military sense of "boundary of a defended position" is attested by 1943. Related: Perimetric; perimetrical.