In Welsh mythology, Blodeuwedd or Blodeuedd, (Middle Welsh composite name from blodeu 'flowers, blossoms' + gwedd 'face, aspect, appearance': "flower face"), is a woman made from the flowers of broom, meadowsweet and the oak by Math fab Mathonwy and Gwydion to be the wife of Lleu Llaw Gyffes. Her story is part of the Fourth Branch of the Mabinogi, the tale of Math son of Mathonwy.
Lleu Llaw Gyffes has been placed under three curses by his mother Arianrhod; the last of these dictates that he will never have a human wife. King Math and Lleu's uncle Gwydion create Blodeuwedd from flowers and she marries Lleu.
Blodeuwedd has an affair with Gronw Pebr and they plot to kill Lleu. Lleu can only be killed under certain conditions, and Blodeuwedd tricks him into telling her what these conditions are. He can not be killed indoors or outdoors, on horseback or on foot; and can be killed only by a spear forged when people are attending mass. Consequently he can only be killed whilst he had one foot on a bathtub and one on a goat (the bathtub being placed on a river bank but under a roof) and by someone using a weapon created as specified.
Under pretence of "Lord, will you show me how these conditions might be fulfilled..?", Blodeuwedd conveys him to precisely this situation, with Gronw lying in wait with the weapon. Lleu is (apparently) killed and Gronw and Blodeuwedd assume power. On hearing of this, Gwydion sets out to find and cure Lleu, who is now in the form of an eagle. Gwydion restores Lleu, who kills Gronw.
Gwydion curses Blodeuwedd, turning her into an owl. "You are never to show your face to the light of day, rather you shall fear other birds; they will be hostile to you, and it will be their nature to maul and molest you wherever they find you. You will not lose your name but always be called Blodeuwedd."

Modern literature
This theonym appears to be derived from Proto-Celtic roots *blāto- and *weid-, together meaning 'flower-face' or 'flower-wild'.