noun 1. a legendary king of the Britons in the sixth century ad, who led Celtic resistance against the Saxons: possibly based on a historical figure; represented as leader of the Knights of the Round Table at Camelot
2. Chester Alan. 1830–86, 21st president of the US (1881–85)
3. (Austral & NZ, informal) not know whether one is Arthur or Martha, to be in a state of confusion