adder's tongue fern vs fern

adder's tongue fern and fern both are nouns.

Word	Noun	Adjective	Verb	Adverb
adder's tongue fern	Yes	No	No	No
fern	Yes	No	No	No

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

adder's tongue fern: ferns with fertile spikes shaped like a snake's tongue
fern: any of numerous flowerless and seedless vascular plants having true roots from a rhizome and fronds that uncurl upward; reproduce by spores

adder's tongue fern (noun)	fern (noun)
ferns with fertile spikes shaped like a snake's tongue	any of numerous flowerless and seedless vascular plants having true roots from a rhizome and fronds that uncurl upward; reproduce by spores