The Collaborative International Dictionary of English v.0.48:

Intercolumniation \In`ter*co*lum`ni*a"tion\, n. (Arch.)
   The clear space between two columns, measured at the bottom
   of their shafts. --Gwilt.
   [1913 Webster]

   Note: It is customary to measure the intercolumniation in
         terms of the diameter of the shaft, taken also at the
         bottom. Different words, derived from the Greek, are in
         use to denote certain common proportions. They are:
         Pycnostyle, when the intercolumniation is of one and
         a half diameters; Systyle, of two diameters;
         Eustyle, of two and a quarter diameters; Diastyle,
         of three diameters; Ar[ae]ostyle, of four or more,
         and so great that a wooden architrave has to be used
         instead of stone; Ar[ae]osystyle, when the
         intercolumniations are alternately systyle and
         ar[ae]ostyle.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Eustyle \Eu"style`\, n. [Gr. ?, neut. of ? with pillars at the
   best distances; e'y^ well + ? pillar: cf. F. eustyle.]
   (Arch.)
   See Intercolumnlation.
   [1913 Webster]