King Arthur
Name

The origin of the Welsh name "Arthur" remains a matter of debate. The most widely accepted etymology derives it from the Roman nomen gentile (family name) Artorius. Artorius itself is of obscure and contested etymology. Linguist Stephan Zimmer suggests Artorius possibly had a Celtic origin, being a Latinization of a hypothetical name *Artorījos, in turn derived from an older patronym *Arto-rīg-ios, meaning "son of the bear/warrior-king". This patronym is unattested, but the root, *arto-rīg, "bear/warrior-king", is the source of the Old Irish personal name Artrí. Some scholars have suggested it is relevant to this debate that the legendary King Arthur's name only appears as Arthur or Arturus in early Latin Arthurian texts, never as Artōrius (though Classical Latin Artōrius became Arturius in some Vulgar Latin dialects). Others believe the origin of the name Arthur, as Artōrius would regularly become Art(h)ur when borrowed into Welsh.

Another commonly proposed derivation of Arthur from Welsh arth "bear" + (g)wr "man" (earlier *Arto-uiros in Brittonic) is not accepted by modern scholars for phonological and orthographic reasons. Notably, a Brittonic compound name *Arto-uiros should produce Old Welsh *Artgur (where u represents the short vowel /u/) and Middle/Modern Welsh *Arthwr, rather than Arthur (where u is a long vowel /ʉː/). In Welsh poetry the name is always spelled Arthur and is exclusively rhymed with words ending in -ur —never words ending in -wr —which confirms that the second element cannot be wr "man".

An alternative theory, which has gained only limited acceptance among professional scholars, derives the name Arthur from Arcturus, the brightest star in the constellation Boötes, near Ursa Major or the Great Bear. Classical Latin Arcturus would also have become Art(h)ur when borrowed into Welsh, and its brightness and position in the sky led people to regard it as the "guardian of the bear" (which is the meaning of the name in Ancient Greek) and the "leader" of the other stars in Boötes.

Many other theories exist, for example that the name has Messapian or Etruscan origins.
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