bird's nest fern vs fern

bird's nest fern and fern both are nouns.

Word	Noun	Adjective	Verb	Adverb
bird's nest fern	Yes	No	No	No
fern	Yes	No	No	No

As nouns, fern is a hypernym of bird's nest fern; that is, fern is a word with a broader meaning than bird's nest fern:

bird's nest fern: tropical Old World or Australian epiphytic fern frequently forming tufts in tree crotches
fern: any of numerous flowerless and seedless vascular plants having true roots from a rhizome and fronds that uncurl upward; reproduce by spores

bird's nest fern (noun)	fern (noun)
tropical Old World or Australian epiphytic fern frequently forming tufts in tree crotches	any of numerous flowerless and seedless vascular plants having true roots from a rhizome and fronds that uncurl upward; reproduce by spores