Art is a Celtic masculine given name, meaning "bear", thus figuratively "champion".
[1] Art meant the ‘bear’ in Celtic languages.
The name derives from Proto-Celtic *artos (“bear”) (compare Cornish arth, Welsh arth, Breton arzh), from Proto-Indo-European *h₂ŕ̥tḱos (“bear”).
With bears the local apex predator, Art figuratively referred to a 'champion', and two legendary High Kings of Ireland had the name, Art mac Cuinn and Art mac Lugdach.
The names Stewart or Stuart can also be shortened to Art, but this is less common.