fern (n.)
Old English fearn, from Proto-Germanic *farno- (cognates: Old Saxon farn, Middle Dutch vaern, Dutch varen, Old High German farn, German Farn), possibly with a sense of "having feathery fronds" and from PIE *por-no-, a root which has yielded words for "feather, wing" (cognates: Sanskrit parnam "feather;" Lithuanian papartis "fern;" Russian paporot'; Greek pteris "fern," pteron "feather"), from root *per- (see petition (n.)). The plant's ability to appear as if from nothing accounts for the ancient belief that fern seeds conferred invisibility.