circumference

Short definition from Wiktionary

Noun

1. 1
   The line that bounds a circle or other two-dimensional figure.
2. 2
   The length of such a line.
3. 3
   The surface of a round or spherical object.
4. 4
   The length of the longest cycle of a graph.

Verb

1. 1
   To include in a circular space; to bound.