Source : Webster's Revised Unabridged Dictionary (1913)

Rationalistic \Ra`tion*al*is"tic\, Rationalistical
\Ra`tion*al*is"tic*al\a.
   Belonging to, or in accordance with, the principles of
   rationalism. -- {Ra`tion*al*is"tic*al*ly}, adv.

Source : WordNet®

rationalistic
     adj : of or relating to the philosophical doctrine of rationalism