Thoughts on words and magic

Words for "magic" abound in Middle Welsh, the most common being hut, distantly related to seið through Indo-European *soito.

Swynwyr is "sorcerer"; sywedydd, prophet or shape-shifter. "Witchcraft" is dewiniaeth, the work of the dewin or "diviner," a word of Latin origin, or, simply the English borrowing, witshkrafft.

Rheibio means "to bewitch" or "to ravage." Middle Welsh kelfyddwr, "artificer," comes from kelfydd, "craft."

Hut is wielded by both Gwydion and Math; but it doesn't exhibit the same kind of negative foregrounding that the Norse give it. Math's punitive magic forces Gwydion and Gilfaethwy not only into animality, but also incest and sodomy. The precise command that "the one who has been the stag last year shall this year be the sow" seems to ensure that both men will suffer the humiliation of being sorðinn. "Great shame" (chywilid mawr) is what Math calls it, "each of you bearing children to the other," in an example of ergi that might compete with Loki's punishments, were it to show any longlasting effects. But where is the vocalized concept of ergi in the Welsh? Does it taint those who make it happen with magic?

From: http://www.illinoismedieval.org/ems/VOL11/11ch10.html