From The Collaborative International Dictionary of English v.0.48 :
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]
From WordNet (r) 3.0 (2006) :
euclidian
adj 1: relating to geometry as developed by Euclid; "Euclidian
geometry" [syn: euclidian, euclidean]