"pertaining to the series of tales of British King Arthur and his knights," 1793, from Arthur + -ian.
Entries linking to arthurian
Arthur
masc. proper name, from Medieval Latin Arthurus/Arturus, usually said to be from Welsh arth "bear," cognate with Greek arktos, Latin ursus (see arctic).
-ian
variant of suffix -an (q.v.), with connective -i-. From Latin -ianus, in which the -i- originally was from the stem of the word being attached but later came to be felt as connective. In Middle English frequently it was -ien, via French.