The Collaborative International Dictionary of English v.0.48:

Circumference \Cir*cum"fer*ence\, n. [L. circumferentia.]
   [1913 Webster]
   1. The line that goes round or encompasses a circular figure;
      a periphery. --Millon.
      [1913 Webster]

   2. A circle; anything circular.
      [1913 Webster]

            His ponderous shield . . .
            Behind him cast. The broad circumference
            Hung on his shoulders like the moon.  --Milton.
      [1913 Webster]

   3. The external surface of a sphere, or of any orbicular
      body.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Circumference \Cir*cum"fer*ence\, v. t.
   To include in a circular space; to bound. [Obs.] --Sir T.
   Browne.
   [1913 Webster]

WordNet (r) 3.0 (2006):

circumference
    n 1: the size of something as given by the distance around it
         [syn: circumference, perimeter]
    2: the boundary line encompassing an area or object; "he had
       walked the full circumference of his land"; "a danger to all
       races over the whole circumference of the globe" [syn:
       circumference, circuit]
    3: the length of the closed curve of a circle

Moby Thesaurus II by Grady Ward, 1.0:

93 Moby Thesaurus words for "circumference":
   O, ambit, annular muscle, annulus, areola, aureole, border,
   boundaries, boundary, bounds, bourns, chaplet, circle, circuit,
   circumscription, circus, closed circle, compass, confines,
   coordinates, corona, coronet, cortex, covering, crown, crust,
   cycle, diadem, discus, disk, edges, envelope, epidermis,
   eternal return, exterior, external, facade, face, facet,
   fairy ring, fringe, fringes, front, garland, glory, halo,
   integument, lasso, limitations, limits, lineaments, logical circle,
   loop, looplet, magic circle, marches, margin, metes,
   metes and bounds, noose, orbit, outer face, outer layer,
   outer side, outer skin, outline, outlines, outside, outskirts,
   pale, parameters, perimeter, periphery, radius, rim, rind, ring,
   rondelle, round, roundel, saucer, shell, skin, skirts, sphincter,
   superficies, superstratum, surface, top, verges, vicious circle,
   wheel, wreath