Tegid Foel was lord of Bala, and husband to Ceridwen.
‘Foel’ means ‘bald’, and this tells us a lot.
The first possible meaning is that it was a nickname. Nicknames are derived from something unusual or noteworthy about the person concerned. An old man being bald is neither unusual nor noteworthy; we can infer that Tegid was not old, and his baldness was unusual. This reinforces my belief that Ceridwen is no hag: she’s a woman in her prime, loving mother to two young children, a witch-queen.
The second possible meaning comes from a Llewellyn Encyclopaedia article on Druid Vestments:
Druids were often described as bald (many had the nickname Mael—Old Irish for “bald”). The bald head was probably a Druidic tonsure, presumably the same kind of partially-shaven head used by later Irish clerics and condemned by the Roman church as non-conformist. This kind of tonsure is made by shaving the hair from ear to ear, along to the front hairline. This gives the appearance of a receding hairline or of a very high forehead. It is interesting to note that Indian Brahmans have a very similar tonsure!
Perhaps, then, this is subtly telling us that Tegid was a Druid!