The Collaborative International Dictionary of English v.0.48:

Isometric \I`so*met"ric\, Isometrical \I`so*met"ric*al\, a.
   [Iso- + Gr. me`tron measure.]
   1. Pertaining to, or characterized by, equality of measure.
      [1913 Webster]

   2. (Crystallog.) Noting, or conforming to, that system of
      crystallization in which the three axes are of equal
      length and at right angles to each other; monometric;
      regular; cubic. Cf. Crystallization.
      [1913 Webster]

   3. Of or pertaining to isometrics.
      [PJC]

   Isometric lines (Thermodynamics), lines representing in a
      diagram the relations of pressure and temperature in a
      gas, when the volume remains constant.

   Isometrical perspective. See under Perspective.

   Isometrical projection, a species of orthographic
      projection, in which but a single plane of projection is
      used. It is so named from the fact that the projections of
      three equal lines, parallel respectively to three
      rectangular axes, are equal to one another. This kind of
      projection is principally used in delineating buildings or
      machinery, in which the principal lines are parallel to
      three rectangular axes, and the principal planes are
      parallel to three rectangular planes passing through the
      three axes.
      [1913 Webster]

WordNet (r) 3.0 (2006):

isometrical
    adj 1: having equal dimensions or measurements [syn:
           isometric, isometrical]