Source : Webster's Revised Unabridged Dictionary (1913)

Euclidian \Eu*clid"i*an\, n.
   Related to Euclid, or to the geometry of Euclid.

   {Euclidian space} (Geom.), the kind of space to which the
      axioms and definitions of Euclid, relative to straight
      lines and parallel lines, apply; -- called also {flat
      space}, and {homaloidal space}.