The clear
space between
two columns, measured at the
bottom of their shafts.
It is customary to
measure the
intercolumniation in terms of the
diameter of the shaft, taken
also at the bottom. Various words, derived from the Greek, are in
use to denote determined
general 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; Araeostyle, of four or more, and so great that a
wooden architrave has to be used instead of stone; Araeosystyle, when the intercolumniations are
alternately systyle and araeostyle.
Source: Websters Vocabulary