Word Origin and History for scilly
isles off Cornwall, of unknown origin. Pliny has Silumnus, Silimnis. Perhaps connected with the Roman god Sulis (cf. Aquae sulis "Bath"). The -y might be Old Norse ey "island" The -c- 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.'" [Victor Watts, "Cambridge Dictionary of English Place-Names," 2004].
Examples from the Web for scilly
It was on the 5th of December that we sighted the Scilly Isles.The Frozen Pirate
W. Clark Russell
It was natural that Tresco should become the ecclesiastical centre of Scilly.
The naval importance of Scilly was fully realised in those days.
Industrially, we chiefly think of Scilly in connection with flowers.
"Scilly people," piped a shrill female voice from our midst.Adventures in Many Lands