The Collaborative International Dictionary of English v.0.48:

Diameter \Di*am"e*ter\, n. [F. diam[`e]tre, L. diametros, fr.
   Gr. ?; dia` through + ? measure. See Meter.]
   1. (Geom.)
      (a) Any right line passing through the center of a figure
          or body, as a circle, conic section, sphere, cube,
          etc., and terminated by the opposite boundaries; a
          straight line which bisects a system of parallel
          chords drawn in a curve.
      (b) A diametral plane.
          [1913 Webster]

   2. The length of a straight line through the center of an
      object from side to side; width; thickness; as, the
      diameter of a tree or rock.
      [1913 Webster]

   Note: In an elongated object the diameter is usually taken at
         right angles to the longer axis.
         [1913 Webster]

   3. (Arch.) The distance through the lower part of the shaft
      of a column, used as a standard measure for all parts of
      the order. See Module.
      [1913 Webster]

   Conjugate diameters. See under Conjugate.
      [1913 Webster]

WordNet (r) 3.0 (2006):

diameter
    n 1: the length of a straight line passing through the center of
         a circle and connecting two points on the circumference
         [syn: diameter, diam]
    2: a straight line connecting the center of a circle with two
       points on its perimeter (or the center of a sphere with two
       points on its surface)

Moby Thesaurus II by Grady Ward, 1.0:

89 Moby Thesaurus words for "diameter":
   air line, amplitude, area, axis, beeline, bigness, bisector, body,
   bore, boundary, breadth, bulk, caliber, center, chord, core,
   coverage, depth, diagonal, diaphragm, dimension, dimensions,
   direct line, directrix, divider, edge, equator, expanse, expansion,
   extension, extent, gauge, girth, great-circle course, greatness,
   halfway mark, heart, height, interior, kernel, largeness, length,
   line of demarcation, magnitude, mass, mean, measure, measurement,
   median, middle, midmost, midriff, midst, normal, nucleus,
   partition, perpendicular, proportion, proportions, radius,
   radius vector, range, reach, right line, scale, scope, secant,
   segment, semidiameter, shortcut, side, size, spread, straight,
   straight course, straight line, straight stretch, straightaway,
   streamline, tangent, thick, thick of things, transversal, vector,
   volume, waist, waistline, width, zone



The Free On-line Dictionary of Computing (30 December 2018):

diameter

   The diameter of a graph is the maximum value of the minimum
   distance between any two nodes.