'Arthurian' originates from Modern English, specifically from the proper name 'Arthur' plus the adjectival suffix '-ian' (from Latin '-ianus'), where 'Arthur' ultimately traces to the Latin name 'Artorius' and a possible Proto-Celtic root 'artos' meaning 'bear'.

'Arthurian' developed from Middle English forms derived from the name 'Arthur' (borrowed into English via Old French/Latin forms of the name), which in turn comes from Latin 'Artorius' and earlier Brittonic/Celtic elements such as 'Artorios' (related to 'artos' meaning 'bear'), eventually forming the Modern English adjective 'Arthurian'.

Initially it meant 'of or pertaining to Arthur (the historical/legendary figure)', but over time it came to mean more broadly 'relating to the legends, literature, cultural motifs, and stylistic features associated with Arthur', extending beyond reference to a single person.