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If Math ap Mathonwy was the brother of the Welsh earth-goddess Dôn and if, as Math’s name suggests, he was the son of Mathonwy, who/what was this Mathonwy? Some kind of primaeval god out which the earth (Dôn) emerged? (Or isn’t there such a story in Welsh mythology?)

Someone on Yahoo!Answers afforded me this helpful insight to the question when s\he said>>
You should note that, although "onwy" usually indicates a male, it is possible that Mathonwy is actually the mother of Math, and that would fit with the generally matrilinear descent.
But surely there's more you can tell me[?]...