Cynwyl Sant is mentioned in the Arthurian romance of Culhwch and Olwen as "the third man that escaped from the Battle of Camlan, and he was the last who parted from Arthur, on Hengroen his horse," the other two being Morfran ab Tegid and Sandde Bryd Angel. (The Lives of British Saints, Baring-Gould, v.2, 1908)

... "hen groen", "old skin", means "an old shit" as a term of abuse by the prudish natives of Arfon (who do not or will not understand its meaning), which may be either an abbreviation of the compound expression, or (by extension) have meant (by itself) simply "a hermaphrodite"; the transition from the peculiar "pellicle" to the creature which it characterized being easy and natural. (Kryptadia, v.2, 1884)