fem. proper name, Old English Eadgyð, from ead "riches, prosperity, good fortune, happiness" + guð "war." A fairly common name; it survived through the Middle Ages, probably on the popularity of St. Eadgyð of Wilton (962-84, abbess, daughter of King Edgar of England), fell from favor 16c., was revived in fashion late 19c. Old English ead (also in eadig "wealthy, prosperous, fortunate, happy, blessed; perfect;" eadnes "inner peace, ease, joy, prosperity") became Middle English edy, eadi "rich, wealthy; costly, expensive; happy, blessed," but was ousted by happy. Late Old English, in its grab-bag of alliterative pairings, had edye men and arme "rich men and poor."
in classical mythology a nymph, mother of Arcas by Zeus, turned to a bear by Hera, from Greek kallistos, superlative of kalos "beautiful, beauteous, noble, good," and its derived noun kallos "beauty," from *kal-wo-, which is of uncertain origin, perhaps related to Sanskrit kalyana "beautiful." The usual combining form in Greek was kalli- "beautiful, fine, happy, favorable;" kalo- was a later, rarer alternative form. Also a name given to the fourth moon of Jupiter in 17c. but not widely used before mid-19c. Feminized as proper name Callista.
isles off Cornwall, a name of unknown origin. Pliny has Silumnus, Silimnis. Perhaps it is connected with the Roman god Sulis (compare Aquae sulis "Bath," literally "waters of Sulis"). The -y might be Old Norse ey "island." The -c- was added 16c.-17c. "[A]bout the only certain thing that can be said is that the c of the modern spelling is not original but was added for distinction from ModE silly as this word developed in meaning from 'happy, blissful' to 'foolish.'" ["Cambridge Dictionary of English Place-Names"].