Euclidian \Eu*clid"i*an\, n. Related to Euclid, or to the geometry of Euclid. [1913 Webster] {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}. [1913 Webster]