(( would be good to know. Pen, head, usually means something like hill in this sort of context; and a Gwern is a boggy place, or by association an alder or similar birch (because they grow in boggy places) or a mast (presumably made of birch wood...). There are places with Alder- or -gwern in the name all over the western side of the Cheshire plain. Pengwern, the court of Cynddylan Wyn, burnt to the ground and celebrated in Canu Heledd, was somewhere in those parts; there is some disagreement about exactly where. g