What is "gwydion"

Gwydion fab Dôn is a magician, hero and trickster of Welsh mythology, appearing most prominently in the Fourth Branch of the Mabinogi, which focuses largely on his relationship with his young nephew, Lleu Llaw Gyffes. He also appears prominently in the Welsh Triads, the Book of Taliesin and the Stanzas of the Graves.

The name Gwydion (which should more properly be spelled Gwyddien in Modern Welsh, as can be adduced from its Old Welsh form Guidgen; cognate with Old Irish Fidgen) may be interpreted as "Born of Trees".