Channel Island, the name is Viking. The second element of the name is Old Norse ey "island" (compare Jersey); the first element uncertain, traditionally meaning "green," but perhaps rather representing a Viking personal name, such as Grani.
Like neighboring Jersey, its name also was taken as the word for a coarse, close-fitting vest of wool (1839), worn originally by seamen, and in Australia the word supplies many of the usages of jersey in U.S. As a type of cattle bred there, from 1784.
1843 as the years of someone's life between 40 and 49; from 1840 as the fifth decade of years in a given century. See forty. Also a designation applied in various places and times to certain oligarchies, ruling classes, or governing bodies.
It is well known that society in the island [Guernsey] is, or perhaps we ought to say, for many years was, divided into two sets, called respectively the Sixties and the Forties, the former composed of the old families and those allied to them, the latter of families of newly-acquired wealth and position. [The Dublin Review, October 1877]
Roaring Forties are rough parts of the ocean between 40 and 50 degrees latitude.