fern (n.) Look up fern at Dictionary.com
Old English fearn "fern," from Proto-Germanic *farno- (cognates: Old Saxon farn, Middle Dutch vaern, Dutch varen, Old High German farn, German Farn).

Possibly the word has a prehistoric sense of "having feathery fronds" and is from PIE *por-no-, which has yielded words for "feather, wing" (cognates: Sanskrit parnam "feather;" Lithuanian papartis "fern;" Russian paporot'; Greek pteris "fern," pteron "feather"), from the root *per- (2) "to lead, pass over" (see petition (n.)). 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."