E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Donegild (3 syl.).
The wicked mother of Alla, King of Northumberland. Hating Cunstance because she was a Christian, she put her on a raft with her infant son, and turned her adrift. When Alla returned from Scotland and discovered this cruelty of his mother, he put her to death. (Chaucer: Man of Lawes Tale.)
The tradition of St. Mungo resembles the Man of Lawes Tale in many respects.