Euterpe

word-forming element, in modern use meaning "good, well," from Greek eus "good," eu "well" (adv.), also "luckily, happily" (opposed to kakos), as a noun, "the right, the good cause," from PIE *(e)su- "good" (source also of Sanskrit su- "good," Avestan hu- "good"), originally a suffixed form of root *es- "to be." In compounds the Greek word had more a sense of "greatness, abundance, prosperity," and was opposed to dys-.

the muse of the dance, Greek Terpsikhore, literally "enjoyment of dance," from terpein "to delight" (from PIE root *terp- "to satisfy;" source also of Sanskrit trpyati "takes one's fill," Lithuanian tarpstu, tarpti "to thrive, prosper") + khoros "dance, chorus" (see chorus).