Meaning

noun (philosophy) the doctrine that knowledge is acquired by reason without resort to experience

noun the theological doctrine that human reason rather than divine revelation establishes religious truth

noun the doctrine that reason is the right basis for regulating conduct

originEtymology tree English rational Proto-Indo-European *-id- Proto-Indo-European *-yéti Proto-Indo-European *-idyéti Proto-Hellenic *-íďďō Ancient Greek -ῐ́ζω (-ĭ́zō) Proto-Indo-European *-mos Proto-Indo-European *-mós Ancient Greek -μός (-mós) Ancient Greek -ισμός (-ismós)der. English -ism English rationalism From rational + -ism.

Etymology from Wiktionary, CC BY-SA 3.0