1580s as a type of knitted cloth; 1842 as a breed of cattle; both from Jersey, one of the Channel Islands. Its name is said to be a corruption of Latin Caesarea, the Roman name for the island (or another near it), influenced by Old English ey "island" (see island); but it is perhaps rather a Viking name (perhaps meaning "Geirr's island").
The meaning "woolen knitted close-fitting tunic," especially one worn during sporting events, is from 1845. In American English, short for New Jersey from 1758. Related: Jerseyman.
Old English fearn "fern," from Proto-Germanic *farno- (source also of Old Saxon farn, Middle Dutch vaern, Dutch varen, Old High German farn, German Farn). Watkins and other sources propose an etymology on the notion of "having feathery fronds" from a possible PIE *por-no- "feather, wing" (source also of Sanskrit parnam "feather, leaf;" Lithuanian papartis "fern;" Russian paporot'; Greek pteris "fern"), a proposed suffixed form of the root *per- (2) "to lead, pass over," on the notion of "that which carries a bird in flight."
The plant's ability to appear as if from nothing accounts for the ancient belief that fern seeds conferred invisibility (1590s). Filicology "science or study of ferns" (1848) is from Latin filix "fern."
"the study of ferns as a branch of botany," 1850, with -logy + from Greek pteris "fern, bracken," probably originally "feather plant," so called for the form of the leaves, and related to pteron "wing" (from PIE root *pet- "to rush, to fly"). Compare fern, also supposed to be descended from a root meaning "feather." Related: Pteridologist (1845).
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.