pillwort vs aquatic fern

pillwort and aquatic fern both are nouns.

Word	Noun	Adjective	Verb	Adverb
pillwort	Yes	No	No	No
aquatic fern	Yes	No	No	No

As nouns, aquatic fern is a hypernym of pillwort; that is, aquatic fern is a word with a broader meaning than pillwort:

pillwort: European water fern found around margins of bodies of water or in wet acid soil having small globose sporocarps
aquatic fern: ferns that grow in water

Other hypernyms of pillwort include water fern.

pillwort (noun)	aquatic fern (noun)
European water fern found around margins of bodies of water or in wet acid soil having small globose sporocarps	ferns that grow in water