Meaning unknown. It first appears in this form in Thomas Malory's 15th-century compilation of Arthurian legends 'Le Morte d'Arthur', in which Gareth was a knight of the Round Table, the brother of Sir Gawain. Malory based the name on Gahariet, which was the name of a similar Arthurian character in French sources. It may ultimately have a Welsh origin, possibly related to gwaredd meaning "gentleness".